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From: Edward Adam Davis <eadavis@qq.com>
To: syzbot+9b8be5e35747291236c8@syzkaller.appspotmail.com
Cc: andrii@kernel.org,
	ast@kernel.org,
	bpf@vger.kernel.org,
	daniel@iogearbox.net,
	haoluo@google.com,
	john.fastabend@gmail.com,
	jolsa@kernel.org,
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	linux-kernel@vger.kernel.org,
	martin.lau@linux.dev,
	sdf@google.com,
	song@kernel.org,
	syzkaller-bugs@googlegroups.com,
	yonghong.song@linux.dev
Subject: [PATCH] bpf: fix uninit-value in strnchr
Date: Tue,  9 Apr 2024 19:37:43 +0800
In-Reply-To: <0000000000009e2ff406130de279@google.com>
References: <0000000000009e2ff406130de279@google.com>
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According to the context in bpf_bprintf_prepare(), this is checking if fmt ends
with a NUL word. Therefore, strnchrnul() should be used for validation instead
of strnchr().

Reported-by: syzbot+9b8be5e35747291236c8@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 kernel/bpf/helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 449b9a5d3fe3..07490eba24fe 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -826,7 +826,7 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
 	u64 cur_arg;
 	char fmt_ptype, cur_ip[16], ip_spec[] = "%pXX";
 
-	fmt_end = strnchr(fmt, fmt_size, 0);
+	fmt_end = strnchrnul(fmt, fmt_size, 0);
 	if (!fmt_end)
 		return -EINVAL;
 	fmt_size = fmt_end - fmt;
-- 
2.43.0