linux-kernel - [PATCH bpf-next] bpf/helpers: bpf

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Message-ID: <tencent_65E5988AD52BEC280D22964189505CD6ED06@qq.com>
Date: Wed, 27 Aug 2025 12:27:23 +0800
From: Rong Tao <rtoax@...mail.com>
To: ast@...nel.org,
	daniel@...earbox.net
Cc: rongtao@...tc.cn,
	rtoax@...mail.com,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	bpf@...r.kernel.org (open list:BPF [GENERAL] (Safe Dynamic Programs and Tools)),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH bpf-next] bpf/helpers: bpf_strnstr: Exact match length

From: Rong Tao <rongtao@...tc.cn>

strnstr should not treat the ending '\0' of s2 as a matching character,
otherwise the parameter 'len' will be meaningless, for example:

    1. bpf_strnstr("openat", "open", 4) = -ENOENT
    2. bpf_strnstr("openat", "open", 5) = 0

This patch makes (1) return 0, indicating a successful match.

Signed-off-by: Rong Tao <rongtao@...tc.cn>
---
 kernel/bpf/helpers.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 401b4932cc49..65bd0050c560 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3681,6 +3681,8 @@ __bpf_kfunc int bpf_strnstr(const char *s1__ign, const char *s2__ign, size_t len
 				return -ENOENT;
 			if (c1 != c2)
 				break;
+			if (j == len - 1)
+				return i;
 		}
 		if (j == XATTR_SIZE_MAX)
 			return -E2BIG;
-- 
2.51.0