Merge tag 'io_uring-5.7-2020-05-22' of git://git.kernel.dk/linux-block

[thirdparty/linux.git] / fs / overlayfs / inode.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *
 * Copyright (C) 2011 Novell Inc.
 */

#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/cred.h>
#include <linux/xattr.h>
#include <linux/posix_acl.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"


int ovl_setattr(struct dentry *dentry, struct iattr *attr)
{
        int err;
        bool full_copy_up = false;
        struct dentry *upperdentry;
        const struct cred *old_cred;

        err = setattr_prepare(dentry, attr);
        if (err)
                return err;

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        if (attr->ia_valid & ATTR_SIZE) {
                struct inode *realinode = d_inode(ovl_dentry_real(dentry));

                err = -ETXTBSY;
                if (atomic_read(&realinode->i_writecount) < 0)
                        goto out_drop_write;

                /* Truncate should trigger data copy up as well */
                full_copy_up = true;
        }

        if (!full_copy_up)
                err = ovl_copy_up(dentry);
        else
                err = ovl_copy_up_with_data(dentry);
        if (!err) {
                struct inode *winode = NULL;

                upperdentry = ovl_dentry_upper(dentry);

                if (attr->ia_valid & ATTR_SIZE) {
                        winode = d_inode(upperdentry);
                        err = get_write_access(winode);
                        if (err)
                                goto out_drop_write;
                }

                if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
                        attr->ia_valid &= ~ATTR_MODE;

                /*
                 * We might have to translate ovl file into real file object
                 * once use cases emerge.  For now, simply don't let underlying
                 * filesystem rely on attr->ia_file
                 */
                attr->ia_valid &= ~ATTR_FILE;

                /*
                 * If open(O_TRUNC) is done, VFS calls ->setattr with ATTR_OPEN
                 * set.  Overlayfs does not pass O_TRUNC flag to underlying
                 * filesystem during open -> do not pass ATTR_OPEN.  This
                 * disables optimization in fuse which assumes open(O_TRUNC)
                 * already set file size to 0.  But we never passed O_TRUNC to
                 * fuse.  So by clearing ATTR_OPEN, fuse will be forced to send
                 * setattr request to server.
                 */
                attr->ia_valid &= ~ATTR_OPEN;

                inode_lock(upperdentry->d_inode);
                old_cred = ovl_override_creds(dentry->d_sb);
                err = notify_change(upperdentry, attr, NULL);
                revert_creds(old_cred);
                if (!err)
                        ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
                inode_unlock(upperdentry->d_inode);

                if (winode)
                        put_write_access(winode);
        }
out_drop_write:
        ovl_drop_write(dentry);
out:
        return err;
}

static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
{
        bool samefs = ovl_same_fs(dentry->d_sb);
        unsigned int xinobits = ovl_xino_bits(dentry->d_sb);
        unsigned int xinoshift = 64 - xinobits;

        if (samefs) {
                /*
                 * When all layers are on the same fs, all real inode
                 * number are unique, so we use the overlay st_dev,
                 * which is friendly to du -x.
                 */
                stat->dev = dentry->d_sb->s_dev;
                return 0;
        } else if (xinobits) {
                /*
                 * All inode numbers of underlying fs should not be using the
                 * high xinobits, so we use high xinobits to partition the
                 * overlay st_ino address space. The high bits holds the fsid
                 * (upper fsid is 0). The lowest xinobit is reserved for mapping
                 * the non-peresistent inode numbers range in case of overflow.
                 * This way all overlay inode numbers are unique and use the
                 * overlay st_dev.
                 */
                if (likely(!(stat->ino >> xinoshift))) {
                        stat->ino |= ((u64)fsid) << (xinoshift + 1);
                        stat->dev = dentry->d_sb->s_dev;
                        return 0;
                } else if (ovl_xino_warn(dentry->d_sb)) {
                        pr_warn_ratelimited("inode number too big (%pd2, ino=%llu, xinobits=%d)\n",
                                            dentry, stat->ino, xinobits);
                }
        }

        /* The inode could not be mapped to a unified st_ino address space */
        if (S_ISDIR(dentry->d_inode->i_mode)) {
                /*
                 * Always use the overlay st_dev for directories, so 'find
                 * -xdev' will scan the entire overlay mount and won't cross the
                 * overlay mount boundaries.
                 *
                 * If not all layers are on the same fs the pair {real st_ino;
                 * overlay st_dev} is not unique, so use the non persistent
                 * overlay st_ino for directories.
                 */
                stat->dev = dentry->d_sb->s_dev;
                stat->ino = dentry->d_inode->i_ino;
        } else {
                /*
                 * For non-samefs setup, if we cannot map all layers st_ino
                 * to a unified address space, we need to make sure that st_dev
                 * is unique per underlying fs, so we use the unique anonymous
                 * bdev assigned to the underlying fs.
                 */
                stat->dev = OVL_FS(dentry->d_sb)->fs[fsid].pseudo_dev;
        }

        return 0;
}

int ovl_getattr(const struct path *path, struct kstat *stat,
                u32 request_mask, unsigned int flags)
{
        struct dentry *dentry = path->dentry;
        enum ovl_path_type type;
        struct path realpath;
        const struct cred *old_cred;
        bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
        int fsid = 0;
        int err;
        bool metacopy_blocks = false;

        metacopy_blocks = ovl_is_metacopy_dentry(dentry);

        type = ovl_path_real(dentry, &realpath);
        old_cred = ovl_override_creds(dentry->d_sb);
        err = vfs_getattr(&realpath, stat, request_mask, flags);
        if (err)
                goto out;

        /*
         * For non-dir or same fs, we use st_ino of the copy up origin.
         * This guaranties constant st_dev/st_ino across copy up.
         * With xino feature and non-samefs, we use st_ino of the copy up
         * origin masked with high bits that represent the layer id.
         *
         * If lower filesystem supports NFS file handles, this also guaranties
         * persistent st_ino across mount cycle.
         */
        if (!is_dir || ovl_same_dev(dentry->d_sb)) {
                if (!OVL_TYPE_UPPER(type)) {
                        fsid = ovl_layer_lower(dentry)->fsid;
                } else if (OVL_TYPE_ORIGIN(type)) {
                        struct kstat lowerstat;
                        u32 lowermask = STATX_INO | STATX_BLOCKS |
                                        (!is_dir ? STATX_NLINK : 0);

                        ovl_path_lower(dentry, &realpath);
                        err = vfs_getattr(&realpath, &lowerstat,
                                          lowermask, flags);
                        if (err)
                                goto out;

                        /*
                         * Lower hardlinks may be broken on copy up to different
                         * upper files, so we cannot use the lower origin st_ino
                         * for those different files, even for the same fs case.
                         *
                         * Similarly, several redirected dirs can point to the
                         * same dir on a lower layer. With the "verify_lower"
                         * feature, we do not use the lower origin st_ino, if
                         * we haven't verified that this redirect is unique.
                         *
                         * With inodes index enabled, it is safe to use st_ino
                         * of an indexed origin. The index validates that the
                         * upper hardlink is not broken and that a redirected
                         * dir is the only redirect to that origin.
                         */
                        if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
                            (!ovl_verify_lower(dentry->d_sb) &&
                             (is_dir || lowerstat.nlink == 1))) {
                                fsid = ovl_layer_lower(dentry)->fsid;
                                stat->ino = lowerstat.ino;
                        }

                        /*
                         * If we are querying a metacopy dentry and lower
                         * dentry is data dentry, then use the blocks we
                         * queried just now. We don't have to do additional
                         * vfs_getattr(). If lower itself is metacopy, then
                         * additional vfs_getattr() is unavoidable.
                         */
                        if (metacopy_blocks &&
                            realpath.dentry == ovl_dentry_lowerdata(dentry)) {
                                stat->blocks = lowerstat.blocks;
                                metacopy_blocks = false;
                        }
                }

                if (metacopy_blocks) {
                        /*
                         * If lower is not same as lowerdata or if there was
                         * no origin on upper, we can end up here.
                         */
                        struct kstat lowerdatastat;
                        u32 lowermask = STATX_BLOCKS;

                        ovl_path_lowerdata(dentry, &realpath);
                        err = vfs_getattr(&realpath, &lowerdatastat,
                                          lowermask, flags);
                        if (err)
                                goto out;
                        stat->blocks = lowerdatastat.blocks;
                }
        }

        err = ovl_map_dev_ino(dentry, stat, fsid);
        if (err)
                goto out;

        /*
         * It's probably not worth it to count subdirs to get the
         * correct link count.  nlink=1 seems to pacify 'find' and
         * other utilities.
         */
        if (is_dir && OVL_TYPE_MERGE(type))
                stat->nlink = 1;

        /*
         * Return the overlay inode nlinks for indexed upper inodes.
         * Overlay inode nlink counts the union of the upper hardlinks
         * and non-covered lower hardlinks. It does not include the upper
         * index hardlink.
         */
        if (!is_dir && ovl_test_flag(OVL_INDEX, d_inode(dentry)))
                stat->nlink = dentry->d_inode->i_nlink;

out:
        revert_creds(old_cred);

        return err;
}

int ovl_permission(struct inode *inode, int mask)
{
        struct inode *upperinode = ovl_inode_upper(inode);
        struct inode *realinode = upperinode ?: ovl_inode_lower(inode);
        const struct cred *old_cred;
        int err;

        /* Careful in RCU walk mode */
        if (!realinode) {
                WARN_ON(!(mask & MAY_NOT_BLOCK));
                return -ECHILD;
        }

        /*
         * Check overlay inode with the creds of task and underlying inode
         * with creds of mounter
         */
        err = generic_permission(inode, mask);
        if (err)
                return err;

        old_cred = ovl_override_creds(inode->i_sb);
        if (!upperinode &&
            !special_file(realinode->i_mode) && mask & MAY_WRITE) {
                mask &= ~(MAY_WRITE | MAY_APPEND);
                /* Make sure mounter can read file for copy up later */
                mask |= MAY_READ;
        }
        err = inode_permission(realinode, mask);
        revert_creds(old_cred);

        return err;
}

static const char *ovl_get_link(struct dentry *dentry,
                                struct inode *inode,
                                struct delayed_call *done)
{
        const struct cred *old_cred;
        const char *p;

        if (!dentry)
                return ERR_PTR(-ECHILD);

        old_cred = ovl_override_creds(dentry->d_sb);
        p = vfs_get_link(ovl_dentry_real(dentry), done);
        revert_creds(old_cred);
        return p;
}

bool ovl_is_private_xattr(const char *name)
{
        return strncmp(name, OVL_XATTR_PREFIX,
                       sizeof(OVL_XATTR_PREFIX) - 1) == 0;
}

int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
                  const void *value, size_t size, int flags)
{
        int err;
        struct dentry *upperdentry = ovl_i_dentry_upper(inode);
        struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
        const struct cred *old_cred;

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        if (!value && !upperdentry) {
                err = vfs_getxattr(realdentry, name, NULL, 0);
                if (err < 0)
                        goto out_drop_write;
        }

        if (!upperdentry) {
                err = ovl_copy_up(dentry);
                if (err)
                        goto out_drop_write;

                realdentry = ovl_dentry_upper(dentry);
        }

        old_cred = ovl_override_creds(dentry->d_sb);
        if (value)
                err = vfs_setxattr(realdentry, name, value, size, flags);
        else {
                WARN_ON(flags != XATTR_REPLACE);
                err = vfs_removexattr(realdentry, name);
        }
        revert_creds(old_cred);

        /* copy c/mtime */
        ovl_copyattr(d_inode(realdentry), inode);

out_drop_write:
        ovl_drop_write(dentry);
out:
        return err;
}

int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
                  void *value, size_t size)
{
        ssize_t res;
        const struct cred *old_cred;
        struct dentry *realdentry =
                ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);

        old_cred = ovl_override_creds(dentry->d_sb);
        res = vfs_getxattr(realdentry, name, value, size);
        revert_creds(old_cred);
        return res;
}

static bool ovl_can_list(const char *s)
{
        /* List all non-trusted xatts */
        if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
                return true;

        /* Never list trusted.overlay, list other trusted for superuser only */
        return !ovl_is_private_xattr(s) &&
               ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);
}

ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
{
        struct dentry *realdentry = ovl_dentry_real(dentry);
        ssize_t res;
        size_t len;
        char *s;
        const struct cred *old_cred;

        old_cred = ovl_override_creds(dentry->d_sb);
        res = vfs_listxattr(realdentry, list, size);
        revert_creds(old_cred);
        if (res <= 0 || size == 0)
                return res;

        /* filter out private xattrs */
        for (s = list, len = res; len;) {
                size_t slen = strnlen(s, len) + 1;

                /* underlying fs providing us with an broken xattr list? */
                if (WARN_ON(slen > len))
                        return -EIO;

                len -= slen;
                if (!ovl_can_list(s)) {
                        res -= slen;
                        memmove(s, s + slen, len);
                } else {
                        s += slen;
                }
        }

        return res;
}

struct posix_acl *ovl_get_acl(struct inode *inode, int type)
{
        struct inode *realinode = ovl_inode_real(inode);
        const struct cred *old_cred;
        struct posix_acl *acl;

        if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
                return NULL;

        old_cred = ovl_override_creds(inode->i_sb);
        acl = get_acl(realinode, type);
        revert_creds(old_cred);

        return acl;
}

int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags)
{
        if (flags & S_ATIME) {
                struct ovl_fs *ofs = inode->i_sb->s_fs_info;
                struct path upperpath = {
                        .mnt = ofs->upper_mnt,
                        .dentry = ovl_upperdentry_dereference(OVL_I(inode)),
                };

                if (upperpath.dentry) {
                        touch_atime(&upperpath);
                        inode->i_atime = d_inode(upperpath.dentry)->i_atime;
                }
        }
        return 0;
}

static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                      u64 start, u64 len)
{
        int err;
        struct inode *realinode = ovl_inode_real(inode);
        const struct cred *old_cred;

        if (!realinode->i_op->fiemap)
                return -EOPNOTSUPP;

        old_cred = ovl_override_creds(inode->i_sb);

        if (fieinfo->fi_flags & FIEMAP_FLAG_SYNC)
                filemap_write_and_wait(realinode->i_mapping);

        err = realinode->i_op->fiemap(realinode, fieinfo, start, len);
        revert_creds(old_cred);

        return err;
}

static const struct inode_operations ovl_file_inode_operations = {
        .setattr        = ovl_setattr,
        .permission     = ovl_permission,
        .getattr        = ovl_getattr,
        .listxattr      = ovl_listxattr,
        .get_acl        = ovl_get_acl,
        .update_time    = ovl_update_time,
        .fiemap         = ovl_fiemap,
};

static const struct inode_operations ovl_symlink_inode_operations = {
        .setattr        = ovl_setattr,
        .get_link       = ovl_get_link,
        .getattr        = ovl_getattr,
        .listxattr      = ovl_listxattr,
        .update_time    = ovl_update_time,
};

static const struct inode_operations ovl_special_inode_operations = {
        .setattr        = ovl_setattr,
        .permission     = ovl_permission,
        .getattr        = ovl_getattr,
        .listxattr      = ovl_listxattr,
        .get_acl        = ovl_get_acl,
        .update_time    = ovl_update_time,
};

static const struct address_space_operations ovl_aops = {
        /* For O_DIRECT dentry_open() checks f_mapping->a_ops->direct_IO */
        .direct_IO              = noop_direct_IO,
};

/*
 * It is possible to stack overlayfs instance on top of another
 * overlayfs instance as lower layer. We need to annotate the
 * stackable i_mutex locks according to stack level of the super
 * block instance. An overlayfs instance can never be in stack
 * depth 0 (there is always a real fs below it).  An overlayfs
 * inode lock will use the lockdep annotaion ovl_i_mutex_key[depth].
 *
 * For example, here is a snip from /proc/lockdep_chains after
 * dir_iterate of nested overlayfs:
 *
 * [...] &ovl_i_mutex_dir_key[depth]   (stack_depth=2)
 * [...] &ovl_i_mutex_dir_key[depth]#2 (stack_depth=1)
 * [...] &type->i_mutex_dir_key        (stack_depth=0)
 *
 * Locking order w.r.t ovl_want_write() is important for nested overlayfs.
 *
 * This chain is valid:
 * - inode->i_rwsem                     (inode_lock[2])
 * - upper_mnt->mnt_sb->s_writers       (ovl_want_write[0])
 * - OVL_I(inode)->lock                 (ovl_inode_lock[2])
 * - OVL_I(lowerinode)->lock            (ovl_inode_lock[1])
 *
 * And this chain is valid:
 * - inode->i_rwsem                     (inode_lock[2])
 * - OVL_I(inode)->lock                 (ovl_inode_lock[2])
 * - lowerinode->i_rwsem                (inode_lock[1])
 * - OVL_I(lowerinode)->lock            (ovl_inode_lock[1])
 *
 * But lowerinode->i_rwsem SHOULD NOT be acquired while ovl_want_write() is
 * held, because it is in reverse order of the non-nested case using the same
 * upper fs:
 * - inode->i_rwsem                     (inode_lock[1])
 * - upper_mnt->mnt_sb->s_writers       (ovl_want_write[0])
 * - OVL_I(inode)->lock                 (ovl_inode_lock[1])
 */
#define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH

static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
{
#ifdef CONFIG_LOCKDEP
        static struct lock_class_key ovl_i_mutex_key[OVL_MAX_NESTING];
        static struct lock_class_key ovl_i_mutex_dir_key[OVL_MAX_NESTING];
        static struct lock_class_key ovl_i_lock_key[OVL_MAX_NESTING];

        int depth = inode->i_sb->s_stack_depth - 1;

        if (WARN_ON_ONCE(depth < 0 || depth >= OVL_MAX_NESTING))
                depth = 0;

        if (S_ISDIR(inode->i_mode))
                lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_dir_key[depth]);
        else
                lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_key[depth]);

        lockdep_set_class(&OVL_I(inode)->lock, &ovl_i_lock_key[depth]);
#endif
}

static void ovl_next_ino(struct inode *inode)
{
        struct ovl_fs *ofs = inode->i_sb->s_fs_info;

        inode->i_ino = atomic_long_inc_return(&ofs->last_ino);
        if (unlikely(!inode->i_ino))
                inode->i_ino = atomic_long_inc_return(&ofs->last_ino);
}

static void ovl_map_ino(struct inode *inode, unsigned long ino, int fsid)
{
        int xinobits = ovl_xino_bits(inode->i_sb);
        unsigned int xinoshift = 64 - xinobits;

        /*
         * When d_ino is consistent with st_ino (samefs or i_ino has enough
         * bits to encode layer), set the same value used for st_ino to i_ino,
         * so inode number exposed via /proc/locks and a like will be
         * consistent with d_ino and st_ino values. An i_ino value inconsistent
         * with d_ino also causes nfsd readdirplus to fail.
         */
        inode->i_ino = ino;
        if (ovl_same_fs(inode->i_sb)) {
                return;
        } else if (xinobits && likely(!(ino >> xinoshift))) {
                inode->i_ino |= (unsigned long)fsid << (xinoshift + 1);
                return;
        }

        /*
         * For directory inodes on non-samefs with xino disabled or xino
         * overflow, we allocate a non-persistent inode number, to be used for
         * resolving st_ino collisions in ovl_map_dev_ino().
         *
         * To avoid ino collision with legitimate xino values from upper
         * layer (fsid 0), use the lowest xinobit to map the non
         * persistent inode numbers to the unified st_ino address space.
         */
        if (S_ISDIR(inode->i_mode)) {
                ovl_next_ino(inode);
                if (xinobits) {
                        inode->i_ino &= ~0UL >> xinobits;
                        inode->i_ino |= 1UL << xinoshift;
                }
        }
}

void ovl_inode_init(struct inode *inode, struct ovl_inode_params *oip,
                    unsigned long ino, int fsid)
{
        struct inode *realinode;

        if (oip->upperdentry)
                OVL_I(inode)->__upperdentry = oip->upperdentry;
        if (oip->lowerpath && oip->lowerpath->dentry)
                OVL_I(inode)->lower = igrab(d_inode(oip->lowerpath->dentry));
        if (oip->lowerdata)
                OVL_I(inode)->lowerdata = igrab(d_inode(oip->lowerdata));

        realinode = ovl_inode_real(inode);
        ovl_copyattr(realinode, inode);
        ovl_copyflags(realinode, inode);
        ovl_map_ino(inode, ino, fsid);
}

static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
        inode->i_mode = mode;
        inode->i_flags |= S_NOCMTIME;
#ifdef CONFIG_FS_POSIX_ACL
        inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
#endif

        ovl_lockdep_annotate_inode_mutex_key(inode);

        switch (mode & S_IFMT) {
        case S_IFREG:
                inode->i_op = &ovl_file_inode_operations;
                inode->i_fop = &ovl_file_operations;
                inode->i_mapping->a_ops = &ovl_aops;
                break;

        case S_IFDIR:
                inode->i_op = &ovl_dir_inode_operations;
                inode->i_fop = &ovl_dir_operations;
                break;

        case S_IFLNK:
                inode->i_op = &ovl_symlink_inode_operations;
                break;

        default:
                inode->i_op = &ovl_special_inode_operations;
                init_special_inode(inode, mode, rdev);
                break;
        }
}

/*
 * With inodes index enabled, an overlay inode nlink counts the union of upper
 * hardlinks and non-covered lower hardlinks. During the lifetime of a non-pure
 * upper inode, the following nlink modifying operations can happen:
 *
 * 1. Lower hardlink copy up
 * 2. Upper hardlink created, unlinked or renamed over
 * 3. Lower hardlink whiteout or renamed over
 *
 * For the first, copy up case, the union nlink does not change, whether the
 * operation succeeds or fails, but the upper inode nlink may change.
 * Therefore, before copy up, we store the union nlink value relative to the
 * lower inode nlink in the index inode xattr trusted.overlay.nlink.
 *
 * For the second, upper hardlink case, the union nlink should be incremented
 * or decremented IFF the operation succeeds, aligned with nlink change of the
 * upper inode. Therefore, before link/unlink/rename, we store the union nlink
 * value relative to the upper inode nlink in the index inode.
 *
 * For the last, lower cover up case, we simplify things by preceding the
 * whiteout or cover up with copy up. This makes sure that there is an index
 * upper inode where the nlink xattr can be stored before the copied up upper
 * entry is unlink.
 */
#define OVL_NLINK_ADD_UPPER     (1 << 0)

/*
 * On-disk format for indexed nlink:
 *
 * nlink relative to the upper inode - "U[+-]NUM"
 * nlink relative to the lower inode - "L[+-]NUM"
 */

static int ovl_set_nlink_common(struct dentry *dentry,
                                struct dentry *realdentry, const char *format)
{
        struct inode *inode = d_inode(dentry);
        struct inode *realinode = d_inode(realdentry);
        char buf[13];
        int len;

        len = snprintf(buf, sizeof(buf), format,
                       (int) (inode->i_nlink - realinode->i_nlink));

        if (WARN_ON(len >= sizeof(buf)))
                return -EIO;

        return ovl_do_setxattr(ovl_dentry_upper(dentry),
                               OVL_XATTR_NLINK, buf, len, 0);
}

int ovl_set_nlink_upper(struct dentry *dentry)
{
        return ovl_set_nlink_common(dentry, ovl_dentry_upper(dentry), "U%+i");
}

int ovl_set_nlink_lower(struct dentry *dentry)
{
        return ovl_set_nlink_common(dentry, ovl_dentry_lower(dentry), "L%+i");
}

unsigned int ovl_get_nlink(struct dentry *lowerdentry,
                           struct dentry *upperdentry,
                           unsigned int fallback)
{
        int nlink_diff;
        int nlink;
        char buf[13];
        int err;

        if (!lowerdentry || !upperdentry || d_inode(lowerdentry)->i_nlink == 1)
                return fallback;

        err = vfs_getxattr(upperdentry, OVL_XATTR_NLINK, &buf, sizeof(buf) - 1);
        if (err < 0)
                goto fail;

        buf[err] = '\0';
        if ((buf[0] != 'L' && buf[0] != 'U') ||
            (buf[1] != '+' && buf[1] != '-'))
                goto fail;

        err = kstrtoint(buf + 1, 10, &nlink_diff);
        if (err < 0)
                goto fail;

        nlink = d_inode(buf[0] == 'L' ? lowerdentry : upperdentry)->i_nlink;
        nlink += nlink_diff;

        if (nlink <= 0)
                goto fail;

        return nlink;

fail:
        pr_warn_ratelimited("failed to get index nlink (%pd2, err=%i)\n",
                            upperdentry, err);
        return fallback;
}

struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev)
{
        struct inode *inode;

        inode = new_inode(sb);
        if (inode)
                ovl_fill_inode(inode, mode, rdev);

        return inode;
}

static int ovl_inode_test(struct inode *inode, void *data)
{
        return inode->i_private == data;
}

static int ovl_inode_set(struct inode *inode, void *data)
{
        inode->i_private = data;
        return 0;
}

static bool ovl_verify_inode(struct inode *inode, struct dentry *lowerdentry,
                             struct dentry *upperdentry, bool strict)
{
        /*
         * For directories, @strict verify from lookup path performs consistency
         * checks, so NULL lower/upper in dentry must match NULL lower/upper in
         * inode. Non @strict verify from NFS handle decode path passes NULL for
         * 'unknown' lower/upper.
         */
        if (S_ISDIR(inode->i_mode) && strict) {
                /* Real lower dir moved to upper layer under us? */
                if (!lowerdentry && ovl_inode_lower(inode))
                        return false;

                /* Lookup of an uncovered redirect origin? */
                if (!upperdentry && ovl_inode_upper(inode))
                        return false;
        }

        /*
         * Allow non-NULL lower inode in ovl_inode even if lowerdentry is NULL.
         * This happens when finding a copied up overlay inode for a renamed
         * or hardlinked overlay dentry and lower dentry cannot be followed
         * by origin because lower fs does not support file handles.
         */
        if (lowerdentry && ovl_inode_lower(inode) != d_inode(lowerdentry))
                return false;

        /*
         * Allow non-NULL __upperdentry in inode even if upperdentry is NULL.
         * This happens when finding a lower alias for a copied up hard link.
         */
        if (upperdentry && ovl_inode_upper(inode) != d_inode(upperdentry))
                return false;

        return true;
}

struct inode *ovl_lookup_inode(struct super_block *sb, struct dentry *real,
                               bool is_upper)
{
        struct inode *inode, *key = d_inode(real);

        inode = ilookup5(sb, (unsigned long) key, ovl_inode_test, key);
        if (!inode)
                return NULL;

        if (!ovl_verify_inode(inode, is_upper ? NULL : real,
                              is_upper ? real : NULL, false)) {
                iput(inode);
                return ERR_PTR(-ESTALE);
        }

        return inode;
}

bool ovl_lookup_trap_inode(struct super_block *sb, struct dentry *dir)
{
        struct inode *key = d_inode(dir);
        struct inode *trap;
        bool res;

        trap = ilookup5(sb, (unsigned long) key, ovl_inode_test, key);
        if (!trap)
                return false;

        res = IS_DEADDIR(trap) && !ovl_inode_upper(trap) &&
                                  !ovl_inode_lower(trap);

        iput(trap);
        return res;
}

/*
 * Create an inode cache entry for layer root dir, that will intentionally
 * fail ovl_verify_inode(), so any lookup that will find some layer root
 * will fail.
 */
struct inode *ovl_get_trap_inode(struct super_block *sb, struct dentry *dir)
{
        struct inode *key = d_inode(dir);
        struct inode *trap;

        if (!d_is_dir(dir))
                return ERR_PTR(-ENOTDIR);

        trap = iget5_locked(sb, (unsigned long) key, ovl_inode_test,
                            ovl_inode_set, key);
        if (!trap)
                return ERR_PTR(-ENOMEM);

        if (!(trap->i_state & I_NEW)) {
                /* Conflicting layer roots? */
                iput(trap);
                return ERR_PTR(-ELOOP);
        }

        trap->i_mode = S_IFDIR;
        trap->i_flags = S_DEAD;
        unlock_new_inode(trap);

        return trap;
}

/*
 * Does overlay inode need to be hashed by lower inode?
 */
static bool ovl_hash_bylower(struct super_block *sb, struct dentry *upper,
                             struct dentry *lower, struct dentry *index)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        /* No, if pure upper */
        if (!lower)
                return false;

        /* Yes, if already indexed */
        if (index)
                return true;

        /* Yes, if won't be copied up */
        if (!ofs->upper_mnt)
                return true;

        /* No, if lower hardlink is or will be broken on copy up */
        if ((upper || !ovl_indexdir(sb)) &&
            !d_is_dir(lower) && d_inode(lower)->i_nlink > 1)
                return false;

        /* No, if non-indexed upper with NFS export */
        if (sb->s_export_op && upper)
                return false;

        /* Otherwise, hash by lower inode for fsnotify */
        return true;
}

static struct inode *ovl_iget5(struct super_block *sb, struct inode *newinode,
                               struct inode *key)
{
        return newinode ? inode_insert5(newinode, (unsigned long) key,
                                         ovl_inode_test, ovl_inode_set, key) :
                          iget5_locked(sb, (unsigned long) key,
                                       ovl_inode_test, ovl_inode_set, key);
}

struct inode *ovl_get_inode(struct super_block *sb,
                            struct ovl_inode_params *oip)
{
        struct dentry *upperdentry = oip->upperdentry;
        struct ovl_path *lowerpath = oip->lowerpath;
        struct inode *realinode = upperdentry ? d_inode(upperdentry) : NULL;
        struct inode *inode;
        struct dentry *lowerdentry = lowerpath ? lowerpath->dentry : NULL;
        bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry,
                                        oip->index);
        int fsid = bylower ? lowerpath->layer->fsid : 0;
        bool is_dir, metacopy = false;
        unsigned long ino = 0;
        int err = oip->newinode ? -EEXIST : -ENOMEM;

        if (!realinode)
                realinode = d_inode(lowerdentry);

        /*
         * Copy up origin (lower) may exist for non-indexed upper, but we must
         * not use lower as hash key if this is a broken hardlink.
         */
        is_dir = S_ISDIR(realinode->i_mode);
        if (upperdentry || bylower) {
                struct inode *key = d_inode(bylower ? lowerdentry :
                                                      upperdentry);
                unsigned int nlink = is_dir ? 1 : realinode->i_nlink;

                inode = ovl_iget5(sb, oip->newinode, key);
                if (!inode)
                        goto out_err;
                if (!(inode->i_state & I_NEW)) {
                        /*
                         * Verify that the underlying files stored in the inode
                         * match those in the dentry.
                         */
                        if (!ovl_verify_inode(inode, lowerdentry, upperdentry,
                                              true)) {
                                iput(inode);
                                err = -ESTALE;
                                goto out_err;
                        }

                        dput(upperdentry);
                        kfree(oip->redirect);
                        goto out;
                }

                /* Recalculate nlink for non-dir due to indexing */
                if (!is_dir)
                        nlink = ovl_get_nlink(lowerdentry, upperdentry, nlink);
                set_nlink(inode, nlink);
                ino = key->i_ino;
        } else {
                /* Lower hardlink that will be broken on copy up */
                inode = new_inode(sb);
                if (!inode) {
                        err = -ENOMEM;
                        goto out_err;
                }
                ino = realinode->i_ino;
                fsid = lowerpath->layer->fsid;
        }
        ovl_fill_inode(inode, realinode->i_mode, realinode->i_rdev);
        ovl_inode_init(inode, oip, ino, fsid);

        if (upperdentry && ovl_is_impuredir(upperdentry))
                ovl_set_flag(OVL_IMPURE, inode);

        if (oip->index)
                ovl_set_flag(OVL_INDEX, inode);

        if (upperdentry) {
                err = ovl_check_metacopy_xattr(upperdentry);
                if (err < 0)
                        goto out_err;
                metacopy = err;
                if (!metacopy)
                        ovl_set_flag(OVL_UPPERDATA, inode);
        }

        OVL_I(inode)->redirect = oip->redirect;

        if (bylower)
                ovl_set_flag(OVL_CONST_INO, inode);

        /* Check for non-merge dir that may have whiteouts */
        if (is_dir) {
                if (((upperdentry && lowerdentry) || oip->numlower > 1) ||
                    ovl_check_origin_xattr(upperdentry ?: lowerdentry)) {
                        ovl_set_flag(OVL_WHITEOUTS, inode);
                }
        }

        if (inode->i_state & I_NEW)
                unlock_new_inode(inode);
out:
        return inode;

out_err:
        pr_warn_ratelimited("failed to get inode (%i)\n", err);
        inode = ERR_PTR(err);
        goto out;
}