netdev - Re: [PATCH net 1/3] skmsg: null check for page in sk_msg

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Date: Mon, 24 Jun 2024 15:54:30 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Geliang Tang <geliang@...nel.org>
Cc: John Fastabend <john.fastabend@...il.com>, Jakub Sitnicki <jakub@...udflare.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	David Ahern <dsahern@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Mykola Lysenko <mykolal@...com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Shuah Khan <shuah@...nel.org>, Mykyta Yatsenko <yatsenko@...a.com>, Miao Xu <miaxu@...a.com>, 
	Yuran Pereira <yuran.pereira@...mail.com>, Geliang Tang <tanggeliang@...inos.cn>, 
	netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net 1/3] skmsg: null check for page in sk_msg_recvmsg

On Mon, Jun 24, 2024 at 3:28 PM Geliang Tang <geliang@...nel.org> wrote:
>
> From: Geliang Tang <tanggeliang@...inos.cn>
>
> Run the following BPF selftests on loongarch:
>
> # ./test_progs -t sockmap_basic
>
> 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-V4.0.11
>  pc 9000000004162774 ra 90000000048bf6c0 tp 90001000aa16c000 sp 90001000aa16fb90
>  a0 0000000000000000 a1 0000000000000000 a2 0000000000000000 a3 90001000aa16fd70
>  a4 0000000000000800 a5 0000000000000000 a6 000055557b63aae8 a7 00000000000000cf
>  t0 0000000000000000 t1 0000000000004000 t2 0000000000000048 t3 0000000000000000
>  t4 0000000000000001 t5 0000000000000002 t6 0000000000000001 t7 0000000000000002
>  t8 0000000000000018 u0 9000000004856150 s9 0000000000000000 s0 0000000000000000
>  s1 0000000000000000 s2 90001000aa16fd70 s3 0000000000000000 s4 0000000000000000
>  s5 0000000000004000 s6 900010009284dc00 s7 0000000000000001 s8 900010009284dc00
>     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=000000001cba0874)
>  Stack : 0000000000000001 fffffffffffffffc 0000000000000000 0000000000000000
>          0000000000000018 0000000000000000 0000000000000000 90000000048bf6c0
>          90000000052cd638 90001000aa16fd70 900010008bf51580 900010009284f000
>          90000000049f2b90 900010009284f188 900010009284f178 90001000861d4780
>          9000100084dccd00 0000000000000800 0000000000000007 fffffffffffffff2
>          000000000453e92f 90000000049aae34 90001000aa16fd60 900010009284f000
>          0000000000000000 0000000000000000 900010008bf51580 90000000049f2b90
>          0000000000000001 0000000000000000 9000100084dc3a10 900010009284f1ac
>          90001000aa16fd40 0000555559953278 0000000000000001 0000000000000000
>          90001000aa16fdc8 9000000005a5a000 90001000861d4780 0000000000000800
>          ...
>  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: 0010b09b  440125a0  0011df8d <28c10364> 0012b70c  00133305  0013b1ac  0010dc84  00151585
>
>  ---[ 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 is because "page" is NULL in that case. This patch adds null
> check for it in sk_msg_recvmsg() to fix this error.
>

Why would @page be NULL only for this architecture ?

Please elaborate, and add a Fixes: tag

> Signed-off-by: Geliang Tang <tanggeliang@...inos.cn>
> ---
>  net/core/skmsg.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> index fd20aae30be2..bafcc1e2eadf 100644
> --- a/net/core/skmsg.c
> +++ b/net/core/skmsg.c
> @@ -432,6 +432,8 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,
>                         sge = sk_msg_elem(msg_rx, i);
>                         copy = sge->length;
>                         page = sg_page(sge);
> +                       if (!page)
> +                               goto out;
>                         if (copied + copy > len)
>                                 copy = len - copied;
>                         copy = copy_page_to_iter(page, sge->offset, copy, iter);
> --
> 2.43.0
>