Re: [syzbot] KASAN: use-after-free Read in rxe_queue_cleanup

Pavel Skripkin
2021-11-20T15:02:13Z

On 11/19/21 12:27, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 8d0112ac6fd0 Merge tag 'net-5.16-rc2' of git://git.kernel...
> git tree: net
> console output: https://syzkaller.appspot.com/x/log.txt?x=14e3eeaab00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=6d3b8fd1977c1e73
> dashboard link: https://syzkaller.appspot.com/bug?extid=aab53008a5adf26abe91
> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+aab53008a5adf26abe91@syzkaller.appspotmail.com
>
> Free swap = 0kB
> Total swap = 0kB
> 2097051 pages RAM
> 0 pages HighMem/MovableOnly
> 384517 pages reserved
> 0 pages cma reserved
> ==================================================================
> BUG: KASAN: use-after-free in rxe_queue_cleanup+0xf4/0x100 drivers/infiniband/sw/rxe/rxe_queue.c:193
> Read of size 8 at addr ffff88814a6b6e90 by task syz-executor.3/9534
>

On error handling path in rxe_qp_from_init() qp->sq.queue is freed and
then rxe_create_qp() will drop last reference to this object. qp clean
up function will try to free this queue one time and it causes UAF bug.

Just for thoughts.

diff --git a/drivers/infiniband/sw/rxe/rxe_qp.c
b/drivers/infiniband/sw/rxe/rxe_qp.c
index 975321812c87..54b8711321c1 100644
--- a/drivers/infiniband/sw/rxe/rxe_qp.c
+++ b/drivers/infiniband/sw/rxe/rxe_qp.c
@@ -359,6 +359,7 @@ int rxe_qp_from_init(struct rxe_dev *rxe, struct
rxe_qp *qp, struct rxe_pd *pd,

err2:
rxe_queue_cleanup(qp->sq.queue);
+ qp->sq.queue = NULL;
err1:
qp->pd = NULL;
qp->rcq = NULL;

With regards,
Pavel Skripkin