linux-kernel - Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

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Message-ID: <tencent_87C9922EC6EEFC8CAD27C0C6C992CE065306@qq.com>
Date: Wed,  7 Jan 2026 16:47:46 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+2c29addf92581b410079@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bpf?] KASAN: slab-out-of-bounds Read in strnchr

#syz test

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index db72b96f9c8c..88da2d0e634c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -827,7 +827,7 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
 	char fmt_ptype, cur_ip[16], ip_spec[] = "%pXX";
 
 	fmt_end = strnchr(fmt, fmt_size, 0);
-	if (!fmt_end)
+	if (!fmt_end || fmt_end == fmt)
 		return -EINVAL;
 	fmt_size = fmt_end - fmt;