linux-ext4 - Re: [PATCH v2] ext4: validate ea_ino and size in check

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Message-Id: <AB6112E6-A3CE-4232-83C6-9099463A7AA4@dilger.ca>
Date: Tue, 23 Sep 2025 12:04:42 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Deepanshu Kartikey <kartikey406@...il.com>
Cc: Theodore Ts'o <tytso@....edu>,
 linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: validate ea_ino and size in check_xattrs

On Sep 23, 2025, at 7:32 AM, Deepanshu Kartikey <kartikey406@...il.com> 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.

This should also have a corresponding check and fix in e2fsck, otherwise
the kernel will fail but there is no way to repair such a filesystem.

Cheers, Andreas

> Suggested-by: Theodore Ts'o <tytso@....edu>
> Reported-by: syzbot+4c9d23743a2409b80293@...kaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?extid=4c9d23743a2409b80293
> Signed-off-by: Deepanshu Kartikey <kartikey406@...il.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
> 


Cheers, Andreas






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