RE: [syzbot] WARNING: suspicious RCU usage in tcp_bpf_update_proto

[John Fastabend]

syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    514e1150 net: x25: Queue received packets in the drivers i..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=112a8831d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=7eff0f22b8563a5f
> dashboard link: https://syzkaller.appspot.com/bug?extid=320a3bc8d80f478c37e4
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1532d711d00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15f44c5ed00000
> 
> The issue was bisected to:
> 
> commit 4dfe6bd94959222e18d512bdf15f6bf9edb9c27c
> Author: Rustam Kovhaev <rkovhaev@xxxxxxxxx>
> Date:   Wed Feb 24 20:00:30 2021 +0000
> 
>     ntfs: check for valid standard information attribute
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16207a81d00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=15207a81d00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11207a81d00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+320a3bc8d80f478c37e4@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 4dfe6bd94959 ("ntfs: check for valid standard information attribute")
> 
> =============================
> WARNING: suspicious RCU usage
> 5.12.0-rc4-syzkaller #0 Not tainted
> -----------------------------
> include/linux/skmsg.h:286 suspicious rcu_dereference_check() usage!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by syz-executor383/8454:
>  #0: ffff888013a99b48 (clock-AF_INET){++..}-{2:2}, at: sk_psock_drop+0x2c/0x460 net/core/skmsg.c:788
> 
> stack backtrace:
> CPU: 1 PID: 8454 Comm: syz-executor383 Not tainted 5.12.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x141/0x1d7 lib/dump_stack.c:120
>  sk_psock include/linux/skmsg.h:286 [inline]
>  tcp_bpf_update_proto+0x530/0x5f0 net/ipv4/tcp_bpf.c:504
>  sk_psock_restore_proto include/linux/skmsg.h:408 [inline]
>  sk_psock_drop+0xdf/0x460 net/core/skmsg.c:789
>  sk_psock_put include/linux/skmsg.h:446 [inline]
>  tcp_bpf_recvmsg+0x42d/0x480 net/ipv4/tcp_bpf.c:208


The bisection is bogus, but we will get a fix for this ASAP. The real commit
is,

commit 8a59f9d1e3d4340659fdfee8879dc09a6f2546e1
Author: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Date:   Tue Mar 30 19:32:31 2021 -0700

    sock: Introduce sk->sk_prot->psock_update_sk_prot()

Thanks,
John