2023-10-03 10:50:58

by Juntong Deng

Subject: [PATCH] fs/jfs: Add checking for out-of-bounds index in binary search in xtSearch

There is currently no out-of-bounds check for the index in a binary
search, which may cause errors.

The following is related bug reported by Syzbot:

UBSAN: array-index-out-of-bounds in fs/jfs/jfs_xtree.c:360:4
index 18 is out of range for type 'xad_t [18]'

Checking if the index exceeds the size of the xad array can solve
this bug.

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=76a072c2f8a60280bd70
Signed-off-by: Juntong Deng <[email protected]>
---
fs/jfs/jfs_xtree.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/fs/jfs/jfs_xtree.c b/fs/jfs/jfs_xtree.c
index 2d304cee884c..6b55bb1e4089 100644
--- a/fs/jfs/jfs_xtree.c
+++ b/fs/jfs/jfs_xtree.c
@@ -356,6 +356,8 @@ static int xtSearch(struct inode *ip, s64 xoff, s64 *nextp,
*/
for (base = XTENTRYSTART; lim; lim >>= 1) {
index = base + (lim >> 1);
+ if (index >= XTROOTMAXSLOT)
+ break;

XT_CMP(cmp, xoff, &p->xad[index], t64);
if (cmp == 0) {
--
2.39.2

2023-10-03 23:37:34

by Dave Kleikamp

Subject: Re: [PATCH] fs/jfs: Add checking for out-of-bounds index in binary search in xtSearch

On 10/3/23 5:49AM, Juntong Deng wrote:
> There is currently no out-of-bounds check for the index in a binary
> search, which may cause errors.
>
> The following is related bug reported by Syzbot:
>
> UBSAN: array-index-out-of-bounds in fs/jfs/jfs_xtree.c:360:4
> index 18 is out of range for type 'xad_t [18]'
>
> Checking if the index exceeds the size of the xad array can solve
> this bug.

This won't work for the same reason I talk about here:
https://sourceforge.net/p/jfs/mailman/message/40826617/

The xad array can be either XTROOTMAXSLOT or XTPAGEMAXSLOT entries long
and it is declared with the smaller number since it's included in the
inode. I will fix the declarations so that we can use the larger number
without triggering code checkers.

Thanks,
Shaggy

>
> Reported-by: [email protected]
> Closes: https://syzkaller.appspot.com/bug?extid=76a072c2f8a60280bd70
> Signed-off-by: Juntong Deng <[email protected]>
> ---
> fs/jfs/jfs_xtree.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/jfs/jfs_xtree.c b/fs/jfs/jfs_xtree.c
> index 2d304cee884c..6b55bb1e4089 100644
> --- a/fs/jfs/jfs_xtree.c
> +++ b/fs/jfs/jfs_xtree.c
> @@ -356,6 +356,8 @@ static int xtSearch(struct inode *ip, s64 xoff, s64 *nextp,
> */
> for (base = XTENTRYSTART; lim; lim >>= 1) {
> index = base + (lim >> 1);
> + if (index >= XTROOTMAXSLOT)
> + break;
>
> XT_CMP(cmp, xoff, &p->xad[index], t64);
> if (cmp == 0) {