cifs: prevent readdir from changing file size due to stale directory metadata

Windows Server's directory enumeration metadata lags behind the actual
file size after a write+close or rename.  A concurrent readdir() in the
window between close() returning to userspace and stat() being called
overwrites the correct cached i_size with the stale server value, causing
stat() to return the wrong size.

Once _cifsFileInfo_put() removes the last writable handle from
openFileList, is_size_safe_to_change() permits readdir to overwrite
i_size.  smb2_close_getattr() then stamps cifs_i->time = jiffies, making
the corrupt cached value appear fresh to the next stat().

The existing check (see Fixes:) only blocked stale size updates while
an active RW lease was held, not after the last writable handle closes.

Add cifsInodeInfo->time_last_write, written via smp_store_release() at
writable close and on setattr/truncate.  is_size_safe_to_change() checks
is_inode_writable() first (acquiring open_file_lock), then rejects a
readdir size update if time_last_write falls within acregmax jiffies.
The spinlock release in _cifsFileInfo_put() forms a store-release barrier
that pairs with the spin_lock() (load-acquire) in is_inode_writable(),
ensuring the subsequent smp_load_acquire() on time_last_write observes
any update from a concurrent close().  When a size update is rejected and
the server value differs from the cached one, cifs_i->time is cleared to
force a fresh QUERY_INFO on the next stat().

readdir is also blocked from changing i_size while writable handles are
open or an RW lease is held, even on direct-IO mounts.

For deferred close (closetimeo > 0), time_last_write is refreshed at the
actual server close in smb2_deferred_work_close() and in the
cifs_close_deferred_file*() drain paths invoked by lease/oplock breaks
and tcon teardown, anchoring the protection window to the real close time
rather than the earlier userspace close.

time_last_write == 0 skips the time_before() check to avoid false
positives near boot on 32-bit systems where jiffies starts close to
INITIAL_JIFFIES.

Does not reproduce against Samba or with actimeo=0.

Fixes: e4b61f3b1c67 ("cifs: prevent updating file size from server if we have a read/write lease")
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index 66b9104e7ca20607111e7dc30e5a84f6e6e68955..1788d93a252246ebb0fae1e8cb7026e04fd7d363 100644 (file)
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -440,6 +440,7 @@ cifs_alloc_inode(struct super_block *sb)
                return NULL;
        cifs_inode->cifsAttrs = ATTR_ARCHIVE;   /* default */
        cifs_inode->time = 0;
+       cifs_inode->time_last_write = 0;
        /*
         * Until the file is open and we have gotten oplock info back from the
         * server, can not assume caching of file data or metadata.

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 08e94633a9c1e28ceacfde197a57d0cc4a938023..79e4e84f8985c9596d8ceb61fdb7918aab14bc99 100644 (file)
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1566,6 +1566,7 @@ struct cifsInodeInfo {
        spinlock_t writers_lock;
        unsigned int writers;           /* Number of writers on this inode */
        unsigned long time;             /* jiffies of last update of inode */
+       unsigned long time_last_write;  /* jiffies of last writable close or truncate */
        u64  uniqueid;                  /* server inode number */
        u64  createtime;                /* creation time on server */
        __u8 lease_key[SMB2_LEASE_KEY_SIZE];    /* lease key for this inode */

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 968740e7c9c3aa71d33aa4b0edbc99dc57ef2175..b279a44be729772f30df3b7309049b572eb32e64 100644 (file)
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -1423,11 +1423,21 @@ void smb2_deferred_work_close(struct work_struct *work)
 {
        struct cifsFileInfo *cfile = container_of(work,
                        struct cifsFileInfo, deferred.work);
+       struct cifsInodeInfo *cinode = CIFS_I(d_inode(cfile->dentry));
 
-       spin_lock(&CIFS_I(d_inode(cfile->dentry))->deferred_lock);
+       spin_lock(&cinode->deferred_lock);
        cifs_del_deferred_close(cfile);
        cfile->deferred_close_scheduled = false;
-       spin_unlock(&CIFS_I(d_inode(cfile->dentry))->deferred_lock);
+       spin_unlock(&cinode->deferred_lock);
+       /*
+        * Refresh time_last_write immediately before the actual server close
+        * so the protection window is anchored to the real close time, not
+        * the earlier userspace close time stored by cifs_close().
+        */
+       if (OPEN_FMODE(cfile->f_flags) & FMODE_WRITE) {
+               /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+               smp_store_release(&cinode->time_last_write, jiffies);
+       }
        _cifsFileInfo_put(cfile, true, false);
 }
 
@@ -1457,6 +1467,10 @@ int cifs_close(struct inode *inode, struct file *file)
        if (file->private_data != NULL) {
                cfile = file->private_data;
                file->private_data = NULL;
+               if (file->f_mode & FMODE_WRITE) {
+                       /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+                       smp_store_release(&cinode->time_last_write, jiffies);
+               }
                dclose = kmalloc_obj(struct cifs_deferred_close);
                if ((cfile->status_file_deleted == false) &&
                    (smb2_can_defer_close(inode, dclose))) {
@@ -3225,13 +3239,26 @@ static int is_inode_writable(struct cifsInodeInfo *cifs_inode)
 bool is_size_safe_to_change(struct cifsInodeInfo *cifsInode, __u64 end_of_file,
                            bool from_readdir)
 {
+       struct cifs_sb_info *cifs_sb;
+       unsigned long tlw;
+
        if (!cifsInode)
                return true;
 
+       cifs_sb = CIFS_SB(cifsInode);
+
        if (is_inode_writable(cifsInode) ||
                ((cifsInode->oplock & CIFS_CACHE_RW_FLG) != 0 && from_readdir)) {
                /* This inode is open for write at least once */
-               struct cifs_sb_info *cifs_sb = CIFS_SB(cifsInode);
+
+               /*
+                * Readdir data is unreliable when we have writable handles or
+                * an exclusive lease -- never allow it to change i_size, even
+                * on direct-IO mounts where the server's directory metadata
+                * can still lag behind the actual file state.
+                */
+               if (from_readdir)
+                       return false;
 
                if (cifs_sb_flags(cifs_sb) & CIFS_MOUNT_DIRECT_IO) {
                        /* since no page cache to corrupt on directio
@@ -3243,8 +3270,40 @@ bool is_size_safe_to_change(struct cifsInodeInfo *cifsInode, __u64 end_of_file,
                        return true;
 
                return false;
-       } else
-               return true;
+       }
+
+       /*
+        * No writable handles open. Check whether we are within the attribute
+        * cache validity window of a recent local modification.
+        *
+        * For the close() path: cifs_close() calls smp_store_release() on
+        * time_last_write before _cifsFileInfo_put() removes the handle under
+        * open_file_lock. That spin_unlock() is a store-release that pairs
+        * with the spin_lock() (load-acquire) in is_inode_writable() above,
+        * so if is_inode_writable() returned false the smp_load_acquire()
+        * below is guaranteed to observe any time_last_write update from a
+        * concurrent close().
+        *
+        * For the setattr/truncate paths: those callers use smp_store_release()
+        * directly; the smp_load_acquire() below pairs with that store. There
+        * is no shared lock between setattr and readdir, so this relies on
+        * acquire-release semantics alone. The store propagation latency on
+        * weakly-ordered architectures (nanoseconds) is negligible relative to
+        * the acregmax window (seconds) and the readdir RPC round-trip
+        * (milliseconds), making this a sound design choice in practice.
+        *
+        * time_last_write == 0 means the inode has never been written locally;
+        * skip the window check to avoid false positives near boot time when
+        * jiffies is still close to INITIAL_JIFFIES on 32-bit systems.
+        */
+       if (from_readdir) {
+               /* Pairs with smp_store_release() at close and truncate sites. */
+               tlw = smp_load_acquire(&cifsInode->time_last_write);
+               if (tlw && time_before(jiffies, tlw + cifs_sb->ctx->acregmax))
+                       return false;
+       }
+
+       return true;
 }
 
 void cifs_oplock_break(struct work_struct *work)

diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index deed04dd9b914fb8a8e743c6d9b8c7491534f9fe..b2806371bfdeaea766613c4e118f1f10be196bca 100644 (file)
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -237,6 +237,8 @@ cifs_fattr_to_inode(struct inode *inode, struct cifs_fattr *fattr,
        if (is_size_safe_to_change(cifs_i, fattr->cf_eof, from_readdir)) {
                i_size_write(inode, fattr->cf_eof);
                inode->i_blocks = CIFS_INO_BLOCKS(fattr->cf_bytes);
+       } else if (from_readdir && i_size_read(inode) != fattr->cf_eof) {
+               cifs_i->time = 0;
        }
 
        if (S_ISLNK(fattr->cf_mode) && fattr->cf_symlink_target) {
@@ -3277,6 +3279,8 @@ cifs_setattr_unix(struct dentry *direntry, struct iattr *attrs)
 
        if ((attrs->ia_valid & ATTR_SIZE) &&
            attrs->ia_size != i_size_read(inode)) {
+               /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+               smp_store_release(&cifsInode->time_last_write, jiffies);
                truncate_setsize(inode, attrs->ia_size);
                netfs_resize_file(&cifsInode->netfs, attrs->ia_size, true);
                fscache_resize_cookie(cifs_inode_cookie(inode), attrs->ia_size);
@@ -3478,6 +3482,8 @@ cifs_setattr_nounix(struct dentry *direntry, struct iattr *attrs)
 
        if ((attrs->ia_valid & ATTR_SIZE) &&
            attrs->ia_size != i_size_read(inode)) {
+               /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+               smp_store_release(&cifsInode->time_last_write, jiffies);
                truncate_setsize(inode, attrs->ia_size);
                netfs_resize_file(&cifsInode->netfs, attrs->ia_size, true);
                fscache_resize_cookie(cifs_inode_cookie(inode), attrs->ia_size);

diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c
index b9c59b2cf76ab05d3e46a3c8d574423a2936e951..fa8cfc4d97f32069368fb3c4726379db27f77e5b 100644 (file)
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -524,7 +524,14 @@ cifs_close_deferred_file(struct cifsInodeInfo *cifs_inode)
        spin_unlock(&cifs_inode->open_file_lock);
 
        list_for_each_entry_safe(tmp_list, tmp_next_list, &file_head, list) {
-               _cifsFileInfo_put(tmp_list->cfile, false, false);
+               struct cifsFileInfo *cfile = tmp_list->cfile;
+
+               if (OPEN_FMODE(cfile->f_flags) & FMODE_WRITE) {
+                       /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+                       smp_store_release(&CIFS_I(d_inode(cfile->dentry))->time_last_write,
+                                         jiffies);
+               }
+               _cifsFileInfo_put(cfile, false, false);
                list_del(&tmp_list->list);
                kfree(tmp_list);
        }
@@ -557,7 +564,14 @@ cifs_close_all_deferred_files(struct cifs_tcon *tcon)
        spin_unlock(&tcon->open_file_lock);
 
        list_for_each_entry_safe(tmp_list, tmp_next_list, &file_head, list) {
-               _cifsFileInfo_put(tmp_list->cfile, true, false);
+               struct cifsFileInfo *cfile = tmp_list->cfile;
+
+               if (OPEN_FMODE(cfile->f_flags) & FMODE_WRITE) {
+                       /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+                       smp_store_release(&CIFS_I(d_inode(cfile->dentry))->time_last_write,
+                                         jiffies);
+               }
+               _cifsFileInfo_put(cfile, true, false);
                list_del(&tmp_list->list);
                kfree(tmp_list);
        }
@@ -626,7 +640,14 @@ void cifs_close_deferred_file_under_dentry(struct cifs_tcon *tcon,
        spin_unlock(&tcon->open_file_lock);
 
        list_for_each_entry_safe(tmp_list, tmp_next_list, &file_head, list) {
-               _cifsFileInfo_put(tmp_list->cfile, true, false);
+               struct cifsFileInfo *cfile = tmp_list->cfile;
+
+               if (OPEN_FMODE(cfile->f_flags) & FMODE_WRITE) {
+                       /* Pairs with smp_load_acquire() in is_size_safe_to_change(). */
+                       smp_store_release(&CIFS_I(d_inode(cfile->dentry))->time_last_write,
+                                         jiffies);
+               }
+               _cifsFileInfo_put(cfile, true, false);
                list_del(&tmp_list->list);
                kfree(tmp_list);
        }