RE: [PATCH bpf] bpf, sockmap: fix an infinite loop error when len is 0 in tcp_bpf_recvmsg_parser()

["liujian (CE)" <liujian56@huawei.com>]

> -----Original Message-----
> From: Alexei Starovoitov [mailto:alexei.starovoitov@gmail.com]
> Sent: Friday, March 3, 2023 3:04 PM
> To: John Fastabend <john.fastabend@gmail.com>
> Cc: liujian (CE) <liujian56@huawei.com>; Eric Dumazet
> <edumazet@google.com>; Jakub Sitnicki <jakub@cloudflare.com>; David S.
> Miller <davem@davemloft.net>; David Ahern <dsahern@kernel.org>; Jakub
> Kicinski <kuba@kernel.org>; Paolo Abeni <pabeni@redhat.com>; Alexei
> Starovoitov <ast@kernel.org>; Cong Wang <cong.wang@bytedance.com>;
> Daniel Borkmann <daniel@iogearbox.net>; Network Development
> <netdev@vger.kernel.org>; bpf <bpf@vger.kernel.org>
> Subject: Re: [PATCH bpf] bpf, sockmap: fix an infinite loop error when len is 0
> in tcp_bpf_recvmsg_parser()
> 
> On Tue, Feb 28, 2023 at 12:36 AM John Fastabend
> <john.fastabend@gmail.com> wrote:
> >
> > Liu Jian wrote:
> > > When the buffer length of the recvmsg system call is 0, we got the
> > > flollowing soft lockup problem:
> > >
> > > watchdog: BUG: soft lockup - CPU#3 stuck for 27s! [a.out:6149]
> > > CPU: 3 PID: 6149 Comm: a.out Kdump: loaded Not tainted 6.2.0+ #30
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1
> > > 04/01/2014
> > > RIP: 0010:remove_wait_queue+0xb/0xc0
> > > Code: 5e 41 5f c3 cc cc cc cc 0f 1f 80 00 00 00 00 90 90 90 90 90 90
> > > 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 41 57 <41>
> > > 56 41 55 41 54 55 48 89 fd 53 48 89 f3 4c 8d 6b 18 4c 8d 73 20
> > > RSP: 0018:ffff88811b5978b8 EFLAGS: 00000246
> > > RAX: 0000000000000000 RBX: ffff88811a7d3780 RCX: ffffffffb7a4d768
> > > RDX: dffffc0000000000 RSI: ffff88811b597908 RDI: ffff888115408040
> > > RBP: 1ffff110236b2f1b R08: 0000000000000000 R09: ffff88811a7d37e7
> > > R10: ffffed10234fa6fc R11: 0000000000000001 R12: ffff88811179b800
> > > R13: 0000000000000001 R14: ffff88811a7d38a8 R15: ffff88811a7d37e0
> > > FS:  00007f6fb5398740(0000) GS:ffff888237180000(0000)
> > > knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 0000000020000000 CR3: 000000010b6ba002 CR4: 0000000000370ee0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > >  <TASK>
> > >  tcp_msg_wait_data+0x279/0x2f0
> > >  tcp_bpf_recvmsg_parser+0x3c6/0x490
> > >  inet_recvmsg+0x280/0x290
> > >  sock_recvmsg+0xfc/0x120
> > >  ____sys_recvmsg+0x160/0x3d0
> > >  ___sys_recvmsg+0xf0/0x180
> > >  __sys_recvmsg+0xea/0x1a0
> > >  do_syscall_64+0x3f/0x90
> > >  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> > >
> > > The logic in tcp_bpf_recvmsg_parser is as follows:
> > >
> > > msg_bytes_ready:
> > >       copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
> > >       if (!copied) {
> > >               wait data;
> > >               goto msg_bytes_ready;
> > >       }
> > >
> > > In this case, "copied" alway is 0, the infinite loop occurs.
> > >
> > > According to the Linux system call man page, 0 should be returned in
> > > this case. Therefore, in tcp_bpf_recvmsg_parser(), if the length is
> > > 0, directly return.
> > >
> > > Also modify several other functions with the same problem.
> > >
> > > Fixes: 1f5be6b3b063 ("udp: Implement udp_bpf_recvmsg() for sockmap")
> > > Fixes: 9825d866ce0d ("af_unix: Implement unix_dgram_bpf_recvmsg()")
> > > Fixes: c5d2177a72a1 ("bpf, sockmap: Fix race in ingress receive
> > > verdict with redirect to self")
> > > Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg
> > > interface")
> > > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > > ---
> >
> > Thanks.
> >
> > Acked-by: John Fastabend <john.fastabend@gmail.com>
> 
> Thanks John.
> 
> Liu,
> 
> could you please change if (len == 0) to if (!len) and respin with John's ack.
> Thanks
Okay, I will send v2. 
Thanks.