Re: [syzbot] [kernel?] KASAN: slab-use-after-free Read in thread_group_cputime

[Pavel Begunkov]

On 1/10/25 13:56, Dmitry Vyukov wrote:
> On Fri, 10 Jan 2025 at 14:51, syzbot
> <syzbot+3d92cfcfa84070b0a470@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    ccb98ccef0e5 Merge tag 'platform-drivers-x86-v6.13-4' of g..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1377fac4580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=1c541fa8af5c9cc7
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3d92cfcfa84070b0a470
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/6e96673b1b94/disk-ccb98cce.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/528385411880/vmlinux-ccb98cce.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/b061a4d50538/bzImage-ccb98cce.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+3d92cfcfa84070b0a470@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > ==================================================================
> > BUG: KASAN: slab-use-after-free in thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341
> > Read of size 8 at addr ffff88803578c510 by task syz.2.3223/27552
> >
> > CPU: 1 UID: 0 PID: 27552 Comm: syz.2.3223 Not tainted 6.13.0-rc5-syzkaller-00004-gccb98ccef0e5 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> > Call Trace:
> >   <TASK>
> >   __dump_stack lib/dump_stack.c:94 [inline]
> >   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
> >   print_address_description mm/kasan/report.c:378 [inline]
> >   print_report+0x169/0x550 mm/kasan/report.c:489
> >   kasan_report+0x143/0x180 mm/kasan/report.c:602
> >   thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341
> >   thread_group_cputime_adjusted+0xa6/0x340 kernel/sched/cputime.c:639
> >   getrusage+0x1000/0x1340 kernel/sys.c:1863
> >   io_uring_show_fdinfo+0xdfe/0x1770 io_uring/fdinfo.c:197
>
> This looks to be more likely an io-uring issue rather than cputime.c
>
> #syz set subsystems: io-uring
>
> +maintainers


Thanks. It probably needs something like below.

diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index 6df5e649c413..5768e31e99b1 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -268,8 +268,12 @@ static int io_sq_thread(void *data)
 	DEFINE_WAIT(wait);
 
 	/* offload context creation failed, just exit */
-	if (!current->io_uring)
+	if (!current->io_uring) {
+		mutex_lock(&sqd->lock);
+		sqd->thread = NULL;
+		mutex_unlock(&sqd->lock);
 		goto err_out;
+	}
 
 	snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
 	set_task_comm(current, buf);

--
Pavel Begunkov