linux-kernel - [PATCH 2/4] bpf: Remove size check for sk in bpf_skb_is_valid

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Date:   Thu, 3 Nov 2022 16:32:52 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
        <john.fastabend@...il.com>, <kpsingh@...nel.org>, <sdf@...gle.com>,
        <haoluo@...gle.com>, <jolsa@...nel.org>,
        <illusionist.neo@...il.com>, <linux@...linux.org.uk>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <mykolal@...com>, <shuah@...nel.org>,
        <benjamin.tissoires@...hat.com>, <memxor@...il.com>,
        <delyank@...com>, <asavkov@...hat.com>, <colin.i.king@...il.com>,
        <bpf@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>
CC:     <yangjihong1@...wei.com>
Subject: [PATCH 2/4] bpf: Remove size check for sk in bpf_skb_is_valid_access for 32-bit architecture

The error code -EACCES is returned when bpf prog is tested in 32-bit environment,
This is because bpf_object__relocate modifies the instruction to change memory
size to 4 bytes, as shown in the following messages:

libbpf: prog 'kfunc_call_test1': relo #2: matching candidate #0 <byte_off> [18342] struct __sk_buff.sk (0:30:0 @ offset 168)
libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) off 168 -> 168
libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) mem_sz 8 -> 4

As a result, the bpf_skb_is_valid_access check fails. For 32-bit architecture,
unnecessary checks need to be deleted.

Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
---
 net/core/filter.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index bb0136e7a8e4..eab7ce89740c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8269,8 +8269,6 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type
 			return false;
 		break;
 	case offsetof(struct __sk_buff, sk):
-		if (type == BPF_WRITE || size != sizeof(__u64))
-			return false;
 		info->reg_type = PTR_TO_SOCK_COMMON_OR_NULL;
 		break;
 	case offsetof(struct __sk_buff, tstamp_type):
-- 
2.30.GIT