[syzbot] [net?] WARNING in inet_sock_destruct (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 45a3e24f65e9 Linux 6.4-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=160cc82f280000
kernel config: https://syzkaller.appspot.com/x/.config?x=2cbd298d0aff1140
dashboard link: https://syzkaller.appspot.com/bug?extid=de6565462ab540f50e47
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=160aacb7280000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17c115d3280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c09bcd4ec365/disk-45a3e24f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/03549b639718/vmlinux-45a3e24f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/91f203e5f63e/bzImage-45a3e24f.xz

The issue was bisected to:

commit 565b4824c39fa335cba2028a09d7beb7112f3c9a
Author: Jiri Pirko <ji...@nvidia.com>
Date: Mon Feb 6 09:41:51 2023 +0000

devlink: change port event netdev notifier from per-net to global

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=110a1a5b280000
final oops: https://syzkaller.appspot.com/x/report.txt?x=130a1a5b280000
console output: https://syzkaller.appspot.com/x/log.txt?x=150a1a5b280000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+de6565...@syzkaller.appspotmail.com
Fixes: 565b4824c39f ("devlink: change port event netdev notifier from per-net to global")

------------[ cut here ]------------
WARNING: CPU: 0 PID: 5025 at net/ipv4/af_inet.c:154 inet_sock_destruct+0x6df/0x8a0 net/ipv4/af_inet.c:154
Modules linked in:
CPU: 0 PID: 5025 Comm: syz-executor250 Not tainted 6.4.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
RIP: 0010:inet_sock_destruct+0x6df/0x8a0 net/ipv4/af_inet.c:154
Code: ff e8 c5 9f e0 f8 0f 0b e9 07 fe ff ff e8 b9 9f e0 f8 0f 0b e9 3f fe ff ff e8 ad 9f e0 f8 0f 0b e9 95 fd ff ff e8 a1 9f e0 f8 <0f> 0b e9 9f fe ff ff e8 d5 6a 33 f9 e9 7a fc ff ff 4c 89 e7 e8 08
RSP: 0018:ffffc90000007de8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 00000000fffff000 RCX: 0000000000000100
RDX: ffff8880792f8000 RSI: ffffffff88a3a73f RDI: 0000000000000005
RBP: ffff88814aa99980 R08: 0000000000000005 R09: 0000000000000000
R10: 00000000fffff000 R11: 0000000000094001 R12: ffff88814aa999a8
R13: ffff88814aa99bf4 R14: ffffc90000007ed8 R15: 0000000000000004
FS: 0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f579b4f6ec8 CR3: 000000000c571000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
__sk_destruct+0x4d/0x770 net/core/sock.c:2130
rcu_do_batch kernel/rcu/tree.c:2115 [inline]
rcu_core+0x806/0x1ad0 kernel/rcu/tree.c:2377
__do_softirq+0x1d4/0x905 kernel/softirq.c:571
invoke_softirq kernel/softirq.c:445 [inline]
__irq_exit_rcu+0x114/0x190 kernel/softirq.c:650
irq_exit_rcu+0x9/0x20 kernel/softirq.c:662
sysvec_apic_timer_interrupt+0x97/0xc0 arch/x86/kernel/apic/apic.c:1106
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
RIP: 0010:write_comp_data+0x3c/0x90 kernel/kcov.c:236
Code: 01 00 00 49 89 f8 65 48 8b 14 25 c0 bb 03 00 a9 00 01 ff 00 74 0e 85 f6 74 59 8b 82 0c 16 00 00 85 c0 74 4f 8b 82 e8 15 00 00 <83> f8 03 75 44 48 8b 82 f0 15 00 00 8b 92 ec 15 00 00 48 8b 38 48
RSP: 0018:ffffc90003a7fbf8 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffffc90003a7b020 RCX: ffffffff814d76d1
RDX: ffff8880792f8000 RSI: 0000000000000000 RDI: 0000000000000007
RBP: ffff8880792f8000 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000094001 R12: 0000000000000000
R13: ffffc90003a78000 R14: dffffc0000000000 R15: ffff8880792f85f8
stack_not_used include/linux/sched/task_stack.h:107 [inline]
check_stack_usage kernel/exit.c:776 [inline]
do_exit+0x17f1/0x29b0 kernel/exit.c:918
do_group_exit+0xd4/0x2a0 kernel/exit.c:1024
get_signal+0x2318/0x25b0 kernel/signal.c:2876
arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x11f/0x240 kernel/entry/common.c:204
__syscall_exit_to_user_mode_work kernel/entry/common.c:286 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:297
do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f579b4a1d39
Code: Unable to access opcode bytes at 0x7f579b4a1d0f.
RSP: 002b:00007f579b431308 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f579b52a4d8 RCX: 00007f579b4a1d39
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f579b52a4d8
RBP: 00007f579b52a4d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f579b4f72c0
R13: 00007f579b52a4dc R14: 00007f579b431400 R15: 0000000000022000
</TASK>
----------------
Code disassembly (best guess):
0: 01 00 add %eax,(%rax)
2: 00 49 89 add %cl,-0x77(%rcx)
5: f8 clc
6: 65 48 8b 14 25 c0 bb mov %gs:0x3bbc0,%rdx
d: 03 00
f: a9 00 01 ff 00 test $0xff0100,%eax
14: 74 0e je 0x24
16: 85 f6 test %esi,%esi
18: 74 59 je 0x73
1a: 8b 82 0c 16 00 00 mov 0x160c(%rdx),%eax
20: 85 c0 test %eax,%eax
22: 74 4f je 0x73
24: 8b 82 e8 15 00 00 mov 0x15e8(%rdx),%eax
* 2a: 83 f8 03 cmp $0x3,%eax <-- trapping instruction
2d: 75 44 jne 0x73
2f: 48 8b 82 f0 15 00 00 mov 0x15f0(%rdx),%rax
36: 8b 92 ec 15 00 00 mov 0x15ec(%rdx),%edx
3c: 48 8b 38 mov (%rax),%rdi
3f: 48 rex.W


---
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[Muhammad Usama Anjum]

This same warning has been spotted and reported:
https://bugzilla.kernel.org/show_bug.cgi?id=217555

Syzbot has found the same warning on 4.14, 5.15, 6.1, 6.5-rc and latest
mainline (1c59d383390f9) kernels. The provided reproducers (such as
https://syzkaller.appspot.com/text?tag=ReproC&x=15a10e8aa80000) are
reproducing the same warnings on multicore (at least 2 CPUs) qemu instance.

--
BR,
Muhammad Usama Anjum

[Eric Dumazet]

Can you test the following fix ?
Thanks.

diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 25816e790527dbd6ff55ffb94762b5974e8144aa..1085357b30c9a0d4bf7a578cebf3eeddec953632
100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -377,8 +377,13 @@ static int dccp_v6_conn_request(struct sock *sk,
struct sk_buff *skb)
if (ipv6_opt_accepted(sk, skb, IP6CB(skb)) ||
np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
+ /* Only initialize ireq->pktops once.
+ * We must take a refcount on skb because ireq->pktops
+ * could be consumed immediately.
+ */
refcount_inc(&skb->users);
- ireq->pktopts = skb;
+ if (cmpxchg(&ireq->pktopts, NULL, skb))
+ refcount_dec(&skb->users);
}
ireq->ir_iif = READ_ONCE(sk->sk_bound_dev_if);

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6e86721e1cdbb8d47b754a2675f6ab1643c7342c..d45aa267473c4ab817cfda06966a536718b50a53
100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -798,8 +798,13 @@ static void tcp_v6_init_req(struct request_sock *req,
np->rxopt.bits.rxinfo ||
np->rxopt.bits.rxoinfo || np->rxopt.bits.rxhlim ||
np->rxopt.bits.rxohlim || np->repflow)) {
+ /* Only initialize ireq->pktops once.
+ * We must take a refcount on skb because ireq->pktops
+ * could be consumed immediately.
+ */
refcount_inc(&skb->users);
- ireq->pktopts = skb;
+ if (cmpxchg(&ireq->pktopts, NULL, skb))
+ refcount_dec(&skb->users);
}
}

[Muhammad Usama Anjum]

Hi Eric,

Just tested the fix on 1c59d383390f9, it didn't fix the warning.

Please let me know if you need help in testing more.

[Eric Dumazet]

On Tue, Aug 29, 2023 at 6:22 PM Muhammad Usama Anjum

Hmm, no more ideas from my side, thanks.