[PATCH v2] erofs-utils: lib: harden h_shared_count in erofs_init_inode_xattrs()

[Gao Xiang]

On 2026/3/17 23:15, Utkal Singh wrote:
> `u8 h_shared_count` indicates the shared xattr count of an inode. It is
> read from the on-disk xattr ibody header, which should be corrupted if
> the size of the shared xattr array exceeds the space available in
> `xattr_isize`.
> 
> It does not cause harmful consequence (e.g. crashes), since the image is
> already considered corrupted, it indeed results in the silent processing
> of garbage metadata.
> 
> Let's harden it to report -EFSCORRUPTED earlier.
> 
> Reproducer:
>    mkdir testdir && echo hello > testdir/a.txt
>    setfattr -n user.test -v val testdir/a.txt
>    mkfs.erofs test.img testdir
>    # corrupt h_shared_count (offset = nid*32 + inode_size + 4) to 0xFF
>    # then: fsck.erofs --extract=/tmp/out --xattrs test_corrupted.img
>    # Without patch: silently processes invalid shared xattr IDs
>    # With patch: returns -EFSCORRUPTED
> 
> Signed-off-by: Utkal Singh <singhutkal015 at gmail.com>
> ---
>   lib/xattr.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/lib/xattr.c b/lib/xattr.c
> index 565070a..9d52a18 100644
> --- a/lib/xattr.c
> +++ b/lib/xattr.c
> @@ -1182,6 +1182,13 @@ static int erofs_init_inode_xattrs(struct erofs_inode *vi)
>   
>   	ih = it.kaddr;
>   	vi->xattr_shared_count = ih->h_shared_count;
> +	if (vi->xattr_shared_count * sizeof(__le32) >
> +	    vi->xattr_isize - sizeof(struct erofs_xattr_ibody_header)) {
> +		erofs_err("invalid h_shared_count %u in nid %llu",

I think this line is incorrect (did you compile at least?), also
you need to Cc LKML <linux-kernel at vger.kernel.org> for all
kernel patches.

Thanks,
Gao Xiang