linux-kernel - [PATCH] bpf: remove pointless code from bpf_do_trace

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Message-Id: <20210421190736.1538217-1-linux@rasmusvillemoes.dk>
Date:   Wed, 21 Apr 2021 21:07:36 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alan Maguire <alan.maguire@...cle.com>,
        Steven Rostedt <rostedt@...dmis.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH] bpf: remove pointless code from bpf_do_trace_printk()

The comment is wrong. snprintf(buf, 16, "") and snprintf(buf, 16,
"%s", "") etc. will certainly put '\0' in buf[0]. The only case where
snprintf() does not guarantee a nul-terminated string is when it is
given a buffer size of 0 (which of course prevents it from writing
anything at all to the buffer).

Remove it before it gets cargo-culted elsewhere.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 kernel/trace/bpf_trace.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index b0c45d923f0f..4ee55df84cd3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -412,9 +412,6 @@ static __printf(1, 0) int bpf_do_trace_printk(const char *fmt, ...)
 	va_start(ap, fmt);
 	ret = vsnprintf(buf, sizeof(buf), fmt, ap);
 	va_end(ap);
-	/* vsnprintf() will not append null for zero-length strings */
-	if (ret == 0)
-		buf[0] = '\0';
 	trace_bpf_trace_printk(buf);
 	raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
 
-- 
2.29.2