Re: [PATCH] bpf/sockmap: fix kernel panic at __tcp_bpf_recvmsg

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Jakub Sitnicki <jakub@cloudflare.com>
Cc: dihu <anny.hu@linux.alibaba.com>, bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>
Subject: Re: [PATCH] bpf/sockmap: fix kernel panic at __tcp_bpf_recvmsg
Date: Tue, 9 Jun 2020 10:58:21 -0700	[thread overview]
Message-ID: <CAADnVQKOyfC8DmxvQuRNayxKErj7xVpZLQALNh+k+w9XrzuRCg@mail.gmail.com> (raw)
In-Reply-To: <874krk391q.fsf@cloudflare.com>

On Tue, Jun 9, 2020 at 2:04 AM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>
> On Fri, Jun 05, 2020 at 10:46 AM CEST, dihu wrote:
> > When user application calls read() with MSG_PEEK flag to read data
> > of bpf sockmap socket, kernel panic happens at
> > __tcp_bpf_recvmsg+0x12c/0x350. sk_msg is not removed from ingress_msg
> > queue after read out under MSG_PEEK flag is set. Because it's not
> > judged whether sk_msg is the last msg of ingress_msg queue, the next
> > sk_msg may be the head of ingress_msg queue, whose memory address of
> > sg page is invalid. So it's necessary to add check codes to prevent
> > this problem.
> >
> > [20759.125457] BUG: kernel NULL pointer dereference, address:
> > 0000000000000008
> > [20759.132118] CPU: 53 PID: 51378 Comm: envoy Tainted: G            E
> > 5.4.32 #1
> > [20759.140890] Hardware name: Inspur SA5212M4/YZMB-00370-109, BIOS
> > 4.1.12 06/18/2017
> > [20759.149734] RIP: 0010:copy_page_to_iter+0xad/0x300
> > [20759.270877] __tcp_bpf_recvmsg+0x12c/0x350
> > [20759.276099] tcp_bpf_recvmsg+0x113/0x370
> > [20759.281137] inet_recvmsg+0x55/0xc0
> > [20759.285734] __sys_recvfrom+0xc8/0x130
> > [20759.290566] ? __audit_syscall_entry+0x103/0x130
> > [20759.296227] ? syscall_trace_enter+0x1d2/0x2d0
> > [20759.301700] ? __audit_syscall_exit+0x1e4/0x290
> > [20759.307235] __x64_sys_recvfrom+0x24/0x30
> > [20759.312226] do_syscall_64+0x55/0x1b0
> > [20759.316852] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > Signed-off-by: dihu <anny.hu@linux.alibaba.com>
> > ---
> >  net/ipv4/tcp_bpf.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> > index 5a05327..b82e4c3 100644
> > --- a/net/ipv4/tcp_bpf.c
> > +++ b/net/ipv4/tcp_bpf.c
> > @@ -64,6 +64,9 @@ int __tcp_bpf_recvmsg(struct sock *sk, struct sk_psock *psock,
> >               } while (i != msg_rx->sg.end);
> >
> >               if (unlikely(peek)) {
> > +                     if (msg_rx == list_last_entry(&psock->ingress_msg,
> > +                                                   struct sk_msg, list))
> > +                             break;
> >                       msg_rx = list_next_entry(msg_rx, list);
> >                       continue;
> >               }
>
> Acked-by: Jakub Sitnicki <jakub@cloudflare.com>

Applied. Thanks