erofs: fix file handle encoding for 64-bit NIDs

EROFS uses NID to indicate the on-disk inode offset, which can
exceed 32 bits. However, the default encode_fh uses the ino32,
thus it doesn't work if the image is larger than 128GiB.

Let's introduce our own helpers to encode file handles.

It's easy to reproduce:
  1. prepare an erofs image with nid bigger than U32_MAX
  2. mount -t erofs foo.img /mnt/erofs
  3. set exportfs with configuration: /mnt/erofs *(rw,sync,
     no_root_squash)
  4. mount -t nfs $IP:/mnt/erofs /mnt/nfs
  5. md5sum /mnt/nfs/foo # foo is the file which nid bigger
     than U32_MAX.  # you will get ESTALE error.

In the case of overlayfs, the underlying filesystem's file
handle is encoded in ovl_fb.fid, which is similar to NFS's
case. If the NID of file is larger than U32_MAX, the overlay
will get -ESTALE error when calls exportfs_decode_fh.

Fixes: 3e917cc305c6 ("erofs: make filesystem exportable")
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250507094015.14007-1-lihongbo22@huawei.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index da6ee7c39290d5083d647444ebf96f35d78abcd9..bcb99c3c2594b387ce7dfe8368107af4c99f291a 100644 (file)
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -510,24 +510,52 @@ static int erofs_fc_parse_param(struct fs_context *fc,
        return 0;
 }
 
-static struct inode *erofs_nfs_get_inode(struct super_block *sb,
-                                        u64 ino, u32 generation)
+static int erofs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
+                          struct inode *parent)
 {
-       return erofs_iget(sb, ino);
+       erofs_nid_t nid = EROFS_I(inode)->nid;
+       int len = parent ? 6 : 3;
+
+       if (*max_len < len) {
+               *max_len = len;
+               return FILEID_INVALID;
+       }
+
+       fh[0] = (u32)(nid >> 32);
+       fh[1] = (u32)(nid & 0xffffffff);
+       fh[2] = inode->i_generation;
+
+       if (parent) {
+               nid = EROFS_I(parent)->nid;
+
+               fh[3] = (u32)(nid >> 32);
+               fh[4] = (u32)(nid & 0xffffffff);
+               fh[5] = parent->i_generation;
+       }
+
+       *max_len = len;
+       return parent ? FILEID_INO64_GEN_PARENT : FILEID_INO64_GEN;
 }
 
 static struct dentry *erofs_fh_to_dentry(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
 {
-       return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
-                                   erofs_nfs_get_inode);
+       if ((fh_type != FILEID_INO64_GEN &&
+            fh_type != FILEID_INO64_GEN_PARENT) || fh_len < 3)
+               return NULL;
+
+       return d_obtain_alias(erofs_iget(sb,
+               ((u64)fid->raw[0] << 32) | fid->raw[1]));
 }
 
 static struct dentry *erofs_fh_to_parent(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
 {
-       return generic_fh_to_parent(sb, fid, fh_len, fh_type,
-                                   erofs_nfs_get_inode);
+       if (fh_type != FILEID_INO64_GEN_PARENT || fh_len < 6)
+               return NULL;
+
+       return d_obtain_alias(erofs_iget(sb,
+               ((u64)fid->raw[3] << 32) | fid->raw[4]));
 }
 
 static struct dentry *erofs_get_parent(struct dentry *child)
@@ -543,7 +571,7 @@ static struct dentry *erofs_get_parent(struct dentry *child)
 }
 
 static const struct export_operations erofs_export_ops = {
-       .encode_fh = generic_encode_ino32_fh,
+       .encode_fh = erofs_encode_fh,
        .fh_to_dentry = erofs_fh_to_dentry,
        .fh_to_parent = erofs_fh_to_parent,
        .get_parent = erofs_get_parent,