Re: [syzbot] [net?] possible deadlock in rtnl_lock (8)

[D. Wythe]

On 9/9/24 7:44 PM, Wenjia Zhang wrote:
> On 09.09.24 10:02, Eric Dumazet wrote:
> > On Sun, Sep 8, 2024 at 10:12 AM syzbot
> > <syzbot+51cf7cc5f9ffc1006ef2@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > > syzbot has found a reproducer for the following issue on:
> > >
> > > HEAD commit:    df54f4a16f82 Merge branch 'for-next/core' into 
> > > for-kernelci
> > > git tree: 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git 
> > > for-kernelci
> > > console output: 
> > > https://syzkaller.appspot.com/x/log.txt?x=12bdabc7980000
> > > kernel config: 
> > > https://syzkaller.appspot.com/x/.config?x=dde5a5ba8d41ee9e
> > > dashboard link: 
> > > https://syzkaller.appspot.com/bug?extid=51cf7cc5f9ffc1006ef2
> > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils 
> > > for Debian) 2.40
> > > userspace arch: arm64
> > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1798589f980000
> > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10a30e00580000
> > >
> > > Downloadable assets:
> > > disk image: 
> > > https://storage.googleapis.com/syzbot-assets/aa2eb06e0aea/disk-df54f4a1.raw.xz
> > > vmlinux: 
> > > https://storage.googleapis.com/syzbot-assets/14728733d385/vmlinux-df54f4a1.xz
> > > kernel image: 
> > > https://storage.googleapis.com/syzbot-assets/99816271407d/Image-df54f4a1.gz.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the 
> > > commit:
> > > Reported-by: syzbot+51cf7cc5f9ffc1006ef2@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > > ======================================================
> > > WARNING: possible circular locking dependency detected
> > > 6.11.0-rc5-syzkaller-gdf54f4a16f82 #0 Not tainted
> > > ------------------------------------------------------
> > > syz-executor272/6388 is trying to acquire lock:
> > > ffff8000923b6ce8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x20/0x2c 
> > > net/core/rtnetlink.c:79
> > >
> > > but task is already holding lock:
> > > ffff0000dc408a50 (&smc->clcsock_release_lock){+.+.}-{3:3}, at: 
> > > smc_setsockopt+0x178/0x10fc net/smc/af_smc.c:3064
> > >
> > > which lock already depends on the new lock.

I have noticed this issue for a while, but I question the possibility of 
it. If I understand correctly, a deadlock issue following is reported here:

#2
lock_sock_smc
{
    clcsock_release_lock            --- deadlock
    {

    }
}

#1
rtnl_mutex
{
    lock_sock_smc
    {

    }
}

#0
clcsock_release_lock
{
    rtnl_mutex                      --deadlock
    {

    }
}

This is of course a deadlock, but #1 is suspicious.

How would this happen to a smc sock?

#1 ->
       lock_sock_nested+0x38/0xe8 net/core/sock.c:3543
       lock_sock include/net/sock.h:1607 [inline]
       sockopt_lock_sock net/core/sock.c:1061 [inline]
       sockopt_lock_sock+0x58/0x74 net/core/sock.c:1052
       do_ip_setsockopt+0xe0/0x2358 net/ipv4/ip_sockglue.c:1078
       ip_setsockopt+0x34/0x9c net/ipv4/ip_sockglue.c:1417
       raw_setsockopt+0x7c/0x2e0 net/ipv4/raw.c:845
       sock_common_setsockopt+0x70/0xe0 net/core/sock.c:3735
       do_sock_setsockopt+0x17c/0x354 net/socket.c:2324

As a comparison, the correct calling chain should be:

       sock_common_setsockopt+0x70/0xe0 net/core/sock.c:3735
       smc_setsockopt+0x150/0xcec net/smc/af_smc.c:3072
       do_sock_setsockopt+0x17c/0x354 net/socket.c:2324


That's to say,  any setting on SOL_IP options of smc_sock will
go with smc_setsockopt, which will try lock clcsock_release_lock at first.

Anyway, if anyone can explain #1, then we can see how to solve this problem,
otherwise I think this problem doesn't exist. (Just my opinion)

Best wishes,
D. Wythe