On Tue, 21 Oct 2025 at 12:48, Stefano Garzarella <[email protected]> wrote: > > On Tue, 21 Oct 2025 at 10:27, Stefano Garzarella <[email protected]> wrote: > > > > Hi Michal, > > > > On Mon, Oct 20, 2025 at 05:02:56PM -0700, syzbot wrote: > > >Hello, > > > > > >syzbot found the following issue on: > > > > > >HEAD commit: d9043c79ba68 Merge tag 'sched_urgent_for_v6.18_rc2' of > > >git.. > > >git tree: upstream > > >console output: https://syzkaller.appspot.com/x/log.txt?x=130983cd980000 > > >kernel config: https://syzkaller.appspot.com/x/.config?x=f3e7b5a3627a90dd > > >dashboard link: > > >https://syzkaller.appspot.com/bug?extid=10e35716f8e4929681fa > > >compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU > > >Binutils for Debian) 2.40 > > >syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17f0f52f980000 > > >C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11ea9734580000 > > > > > >Downloadable assets: > > >disk image (non-bootable): > > >https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-d9043c79.raw.xz > > >vmlinux: > > >https://storage.googleapis.com/syzbot-assets/0546b6eaf1aa/vmlinux-d9043c79.xz > > >kernel image: > > >https://storage.googleapis.com/syzbot-assets/81285b4ada51/bzImage-d9043c79.xz > > > > > >IMPORTANT: if you fix the issue, please add the following tag to the > > >commit: > > >Reported-by: [email protected] > > > > > >====================================================== > > >WARNING: possible circular locking dependency detected > > >syzkaller #0 Not tainted > > >------------------------------------------------------ > > >syz.0.17/6098 is trying to acquire lock: > > >ffff8880363b8258 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: lock_sock > > >include/net/sock.h:1679 [inline] > > >ffff8880363b8258 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: > > >vsock_linger+0x25e/0x4d0 net/vmw_vsock/af_vsock.c:1066 > > > > Could this be related to our recent work on linger in vsock? > > > > > > > >but task is already holding lock: > > >ffffffff906260a8 (vsock_register_mutex){+.+.}-{4:4}, at: > > >vsock_assign_transport+0xf2/0x900 net/vmw_vsock/af_vsock.c:469 > > > > > >which lock already depends on the new lock. > > > > > > > > >the existing dependency chain (in reverse order) is: > > > > > >-> #1 (vsock_register_mutex){+.+.}-{4:4}: > > > __mutex_lock_common kernel/locking/mutex.c:598 [inline] > > > __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760 > > > vsock_registered_transport_cid net/vmw_vsock/af_vsock.c:560 [inline] > > > > Ah, no maybe this is related to commit 209fd720838a ("vsock: > > Fix transport_{g2h,h2g} TOCTOU") where we added locking in > > vsock_find_cid(). > > > > Maybe we can just move the checks on top of __vsock_bind() to the > > caller. I mean: > > > > /* First ensure this socket isn't already bound. */ > > if (vsock_addr_bound(&vsk->local_addr)) > > return -EINVAL; > > > > /* Now bind to the provided address or select appropriate values if > > * none are provided (VMADDR_CID_ANY and VMADDR_PORT_ANY). Note > > that > > * like AF_INET prevents binding to a non-local IP address (in most > > * cases), we only allow binding to a local CID. > > */ > > if (addr->svm_cid != VMADDR_CID_ANY && > > !vsock_find_cid(addr->svm_cid)) > > return -EADDRNOTAVAIL; > > > > We have 2 callers: vsock_auto_bind() and vsock_bind(). > > > > vsock_auto_bind() is already checking if the socket is already bound, > > if not is setting VMADDR_CID_ANY, so we can skip those checks. > > > > In vsock_bind() we can do the checks before lock_sock(sk), at least the > > checks on vm_addr, calling vsock_find_cid(). > > > > I'm preparing a patch to do this. > > mmm, no, this is more related to vsock_linger() where sk_wait_event() > releases and locks again the sk_lock. > So, it should be related to commit 687aa0c5581b ("vsock: Fix > transport_* TOCTOU") where we take vsock_register_mutex in > vsock_assign_transport() while calling vsk->transport->release(). > > So, maybe we need to move the release and vsock_deassign_transport() > after unlocking vsock_register_mutex.
I implemented this here: https://lore.kernel.org/netdev/[email protected]/ sysbot successfully tested it. Stefano
