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SubjectRe: [PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG
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On 10/19/22 4:38AM, Hoi Pok Wu wrote:
> Bug reported by syzbot, UBSAN: array-index-out-of-bounds in dbDiscardAG.
> Fixed by simply rearranging agno_end smaller than MAXAG. However, I wonder if it
> is a better idea to return -EINVAL, rejecting user input. Thank you.

I don't think the problem is simply that the user input is bad, the
range is already limited:

if (end >= bmp->db_mapsize)
end = bmp->db_mapsize - 1;

It seems syzbot corrupted some on-disk data structure to trigger this
failure. It may be best to call jfs_error() and bail out.

Thanks,
Shaggy

>
> Reported-by: syzbot+f0e0fcf3cd1047ae60ad@syzkaller.appspotmail.com
> Signed-off-by: Hoi Pok Wu <wuhoipok@gmail.com>
> ---
> fs/jfs/jfs_discard.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/fs/jfs/jfs_discard.c b/fs/jfs/jfs_discard.c
> index 575cb2ba74fc..3101eaf3098a 100644
> --- a/fs/jfs/jfs_discard.c
> +++ b/fs/jfs/jfs_discard.c
> @@ -96,6 +96,10 @@ int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range)
> */
> agno = BLKTOAG(start, JFS_SBI(ip->i_sb));
> agno_end = BLKTOAG(end, JFS_SBI(ip->i_sb));
> +
> + if (agno_end >= MAXAG)
> + agno_end = MAXAG - 1;
> +
> while (agno <= agno_end) {
> trimmed += dbDiscardAG(ip, agno, minlen);
> agno++;

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