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

From: Jakub Sitnicki <jakub@cloudflare.com>
To: dihu <anny.hu@linux.alibaba.com>
Cc: bpf@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH] bpf/sockmap: fix kernel panic at __tcp_bpf_recvmsg
Date: Tue, 09 Jun 2020 11:03:45 +0200	[thread overview]
Message-ID: <874krk391q.fsf@cloudflare.com> (raw)
In-Reply-To: <20200605084625.9783-1-anny.hu@linux.alibaba.com>

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>