During xattr block validation, check_xattrs() processes xattr entries
without validating that entries claiming to use EA inodes have non-zero
sizes. Corrupted filesystems may contain xattr entries where e_value_size
is zero but e_value_inum is non-zero, indicating invalid xattr data.

Add validation in check_xattrs() to detect this corruption pattern early
and return -EFSCORRUPTED, preventing invalid xattr entries from causing
issues throughout the ext4 codebase.

Suggested-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: syzbot+4c9d23743a2409b80293@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=4c9d23743a2409b80293
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
---
Changes in v2:
- Moved validation from ext4_xattr_move_to_block() to check_xattrs() as suggested by Theodore Ts'o
- This provides broader coverage and may address other similar syzbot reports

 fs/ext4/xattr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 5a6fe1513fd2..d621e77c8c4d 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -251,6 +251,10 @@ check_xattrs(struct inode *inode, struct buffer_head *bh,
 			err_str = "invalid ea_ino";
 			goto errout;
 		}
+		if (ea_ino && !size) {
+			err_str = "invalid size in ea xattr";
+			goto errout;
+		}
 		if (size > EXT4_XATTR_SIZE_MAX) {
 			err_str = "e_value size too large";
 			goto errout;
-- 
2.43.0

On Tue, 23 Sep 2025 19:02:45 +0530, Deepanshu Kartikey wrote:
> During xattr block validation, check_xattrs() processes xattr entries
> without validating that entries claiming to use EA inodes have non-zero
> sizes. Corrupted filesystems may contain xattr entries where e_value_size
> is zero but e_value_inum is non-zero, indicating invalid xattr data.
> 
> Add validation in check_xattrs() to detect this corruption pattern early
> and return -EFSCORRUPTED, preventing invalid xattr entries from causing
> issues throughout the ext4 codebase.
> 
> [...]

Applied, thanks!

[1/1] ext4: validate ea_ino and size in check_xattrs
      commit: 44d2a72f4d64655f906ba47a5e108733f59e6f28

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>