ext4: validate ea_ino and size in check_xattrs

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.

Cc: stable@kernel.org
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>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Message-ID: <20250923133245.1091761-1-kartikey406@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: deepanshu406

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;