Re: [syzbot] [net?] possible deadlock in inet6_getname

[Gerd Rausch <gerd.rausch@oracle.com>]

Hi,

On 2026-02-13 09:26, Eric Dumazet wrote:
> On Fri, Feb 13, 2026 at 1:15 PM syzbot
> <syzbot+5efae91f60932839f0a5@syzkaller.appspotmail.com> wrote:
>>
>>
[...]
>> ============================================
>> WARNING: possible recursive locking detected
>> syzkaller #0 Not tainted
>> --------------------------------------------
>> kworker/u8:6/2985 is trying to acquire lock:
>> ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1709 [inline]
>> ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet6_getname+0x15d/0x650 net/ipv6/af_inet6.c:533
>>
>> but task is already holding lock:
>> ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1709 [inline]
>> ffff88807a07aa20 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: tcp_sock_set_cork+0x2c/0x2e0 net/ipv4/tcp.c:3694
>>
[...]
>>   lock_sock_nested+0x48/0x100 net/core/sock.c:3780
>>   lock_sock include/net/sock.h:1709 [inline]
>>   inet6_getname+0x15d/0x650 net/ipv6/af_inet6.c:533
>>   rds_tcp_get_peer_sport net/rds/tcp_listen.c:70 [inline]
>>   rds_tcp_conn_slots_available+0x288/0x470 net/rds/tcp_listen.c:149
>>   rds_recv_hs_exthdrs+0x60f/0x7c0 net/rds/recv.c:265
>>   rds_recv_incoming+0x9f6/0x12d0 net/rds/recv.c:389
>>   rds_tcp_data_recv+0x7f1/0xa40 net/rds/tcp_recv.c:243
>>   __tcp_read_sock+0x196/0x970 net/ipv4/tcp.c:1702
>>   rds_tcp_read_sock net/rds/tcp_recv.c:277 [inline]
>>   rds_tcp_data_ready+0x369/0x950 net/rds/tcp_recv.c:331
>>   tcp_rcv_established+0x19e9/0x2670 net/ipv4/tcp_input.c:6675
>>   tcp_v6_do_rcv+0x8eb/0x1ba0 net/ipv6/tcp_ipv6.c:1609
>>   sk_backlog_rcv include/net/sock.h:1185 [inline]
>>   __release_sock+0x1b8/0x3a0 net/core/sock.c:3213
> 
[...]
> Gerd, please take a look, thanks.
> 
> commit 9d27a0fb122f19b6d01d02f4b4f429ca28811ace
> Author: Gerd Rausch <gerd.rausch@oracle.com>
> Date:   Mon Feb 2 22:57:23 2026 -0700
> 
>      net/rds: Trigger rds_send_ping() more than once

Syzbot is right:

inet_getname() acquires a lock_sock() that was already held
as __release_sock() is about to give it up, but before
doing so, handles the backlog receives & callbacks.

Just need to figure out a way to obtain the peer's port number,
without ending up in such a recursive lock scenario.

Thanks for forwarding this,

   Gerd