On 6/26/23 2:15 AM, Michael S. Tsirkin wrote: > On Mon, Jun 26, 2023 at 12:06:54AM -0700, syzbot wrote: >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 8d2be868b42c Add linux-next specific files for 20230623 >> git tree: linux-next >> console+strace: https://syzkaller.appspot.com/x/log.txt?x=12872950a80000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=d8ac8dd33677e8e0 >> dashboard link: https://syzkaller.appspot.com/bug?extid=8540db210d403f1aa214 >> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15c1b70f280000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=122ee4cb280000 >> >> Downloadable assets: >> disk image: https://storage.googleapis.com/syzbot-assets/2a004483aca3/disk-8d2be868.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/5688cb13b277/vmlinux-8d2be868.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/76de0b63bc53/bzImage-8d2be868.xz >> >> The issue was bisected to: >> >> commit 21a18f4a51896fde11002165f0e7340f4131d6a0 >> Author: Mike Christie <michael.christie@xxxxxxxxxx> >> Date: Tue Jun 13 01:32:46 2023 +0000 >> >> vhost: allow userspace to create workers >> >> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=130850bf280000 >> final oops: https://syzkaller.appspot.com/x/report.txt?x=108850bf280000 >> console output: https://syzkaller.appspot.com/x/log.txt?x=170850bf280000 >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+8540db210d403f1aa214@xxxxxxxxxxxxxxxxxxxxxxxxx >> Fixes: 21a18f4a5189 ("vhost: allow userspace to create workers") > > Mike, would appreciate prompt attention to this as I am preparing > a pull request for the merge window and need to make a > decision on whether to include your userspace-controlled > threading patchset. > Do you want me to resubmit the patchset or submit a patch against your vhost branch? The bug is that vhost-net can call vhost_dev_reset_owner and that will free the workers. However, I leave the virtqueue->worker pointer set so we end up referencing the freed workers later on. When I handled a review comment between v5 and v6, I deleted that code thinking it was also not needed. So the fix is: diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index ab79b064aade..5a07e220e46d 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -607,6 +607,10 @@ static void vhost_workers_free(struct vhost_dev *dev) if (!dev->use_worker) return; + + for (i = 0; i < dev->nvqs; i++) + rcu_assign_pointer(dev->vqs[i]->worker, NULL); + /* * Free the default worker we created and cleanup workers userspace * created but couldn't clean up (it forgot or crashed).
