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

On Tue, Apr 6, 2021 at 2:44 AM syzbot
[off-list ref] 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 [off-list ref]
Date:   Wed Feb 24 20:00:30 2021 +0000

    ntfs: check for valid standard information attribute

This is caused by one of my sockmap patches.

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@syzkaller.appspotmail.com
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
 inet_recvmsg+0x11b/0x5d0 net/ipv4/af_inet.c:852

Oddly, I have all relevant Kconfig enabled but never see this
warning when running selftests for hours....

Anyway, let me see how this should be fixed.

Thanks!