[PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG

[PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG

[Hoi Pok Wu]

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.

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++;
-- 
2.38.0

Re: [PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG

[Dave Kleikamp]

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++;

Re: [PATCH] fs: jfs: fix shift-out-of-bounds in dbDiscardAG

[Hoi Pok Wu]

Thanks for the suggestion! I will send a Patch V2 soon.


On Tue, Oct 25, 2022 at 5:05 AM Dave Kleikamp <dave.kleikamp@oracle.com> wrote:
>
> 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++;