Re: [PATCH net v3 1/2] skmsg: prevent empty ingress skb from enqueuing

["D. Wythe" <alibuda@linux.alibaba.com>]

On 6/28/24 1:47 PM, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
>
> Run this BPF selftests (./test_progs -t sockmap_basic) on a Loongarch
> platform, a Kernel panic occurs:
>
> '''
> Oops[#1]:
> CPU: 22 PID: 2824 Comm: test_progs Tainted: G           OE  6.10.0-rc2+ #18
> Hardware name: LOONGSON Dabieshan/Loongson-TC542F0, BIOS Loongson-UDK2018
>     ... ...
>     ra: 90000000048bf6c0 sk_msg_recvmsg+0x120/0x560
>    ERA: 9000000004162774 copy_page_to_iter+0x74/0x1c0
>   CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
>   PRMD: 0000000c (PPLV0 +PIE +PWE)
>   EUEN: 00000007 (+FPE +SXE +ASXE -BTE)
>   ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
> ESTAT: 00010000 [PIL] (IS= ECode=1 EsubCode=0)
>   BADV: 0000000000000040
>   PRID: 0014c011 (Loongson-64bit, Loongson-3C5000)
> Modules linked in: bpf_testmod(OE) xt_CHECKSUM xt_MASQUERADE xt_conntrack
> Process test_progs (pid: 2824, threadinfo=0000000000863a31, task=...)
> Stack : ...
>          ...
> Call Trace:
> [<9000000004162774>] copy_page_to_iter+0x74/0x1c0
> [<90000000048bf6c0>] sk_msg_recvmsg+0x120/0x560
> [<90000000049f2b90>] tcp_bpf_recvmsg_parser+0x170/0x4e0
> [<90000000049aae34>] inet_recvmsg+0x54/0x100
> [<900000000481ad5c>] sock_recvmsg+0x7c/0xe0
> [<900000000481e1a8>] __sys_recvfrom+0x108/0x1c0
> [<900000000481e27c>] sys_recvfrom+0x1c/0x40
> [<9000000004c076ec>] do_syscall+0x8c/0xc0
> [<9000000003731da4>] handle_syscall+0xc4/0x160
>
> Code: ...
>
> ---[ end trace 0000000000000000 ]---
> Kernel panic - not syncing: Fatal exception
> Kernel relocated by 0x3510000
>   .text @ 0x9000000003710000
>   .data @ 0x9000000004d70000
>   .bss  @ 0x9000000006469400
> ---[ end Kernel panic - not syncing: Fatal exception ]---
> '''
>
> This crash happens every time when running sockmap_skb_verdict_shutdown
> subtest in sockmap_basic.
>
> This crash is because a NULL pointer is passed to page_address() in
> sk_msg_recvmsg(). Due to the difference in architecture, page_address(0)
> will not trigger a panic on the X86 platform but will panic on the
> Loogarch platform. So this bug was hidden on the x86 platform, but now
> it is exposed on the Loogarch platform.

Maybe Loongarch ?  Besides that, LGTM.
Reviewed-by: D. Wythe <alibuda@linux.alibaba.com>

>
> The root cause is an empty skb (skb->len == 0) is put on the queue.
>
> In this case, in sk_psock_skb_ingress_enqueue(), num_sge is zero, and no
> page is put to this sge (see sg_set_page in sg_set_page), but this empty
> sge is queued into ingress_msg list.
>
> And in sk_msg_recvmsg(), this empty sge is used, and a NULL page is
> got by sg_page(sge). Pass this NULL-page to copy_page_to_iter(), it
> passed to kmap_local_page() and page_address(), then kernel panics.
>
> To solve this, we should prevent empty skb from putting on the queue. So
> in sk_psock_verdict_recv(), if the skb->len is zero, drop this skb.
>
> Fixes: ef5659280eb1 ("bpf, sockmap: Allow skipping sk_skb parser program")
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> ---
>   net/core/skmsg.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> index fd20aae30be2..44952cdd1425 100644
> --- a/net/core/skmsg.c
> +++ b/net/core/skmsg.c
> @@ -1184,7 +1184,7 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
>   
>   	rcu_read_lock();
>   	psock = sk_psock(sk);
> -	if (unlikely(!psock)) {
> +	if (unlikely(!psock || !len)) {
>   		len = 0;
>   		tcp_eat_skb(sk, skb);
>   		sock_drop(sk, skb);