From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Date: Wed, 26 Nov 2014 15:05:41 +0000 Subject: Re: [patch] tracing: off by one in __trace_array_vprintk() Message-Id: <20141126150541.GU4893@mwanda> List-Id: References: <20141126140621.GA18740@mwanda> <20141126092706.5d4038d4@gandalf.local.home> <20141126143719.GT4893@mwanda> <20141126094306.4f465616@gandalf.local.home> In-Reply-To: <20141126094306.4f465616@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Steven Rostedt Cc: Ingo Molnar , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org On Wed, Nov 26, 2014 at 09:43:06AM -0500, Steven Rostedt wrote: > I highly doubt it's much of a speed up. And we do that by sacrificing > that one byte of buffer, which would lose the printk if len does equal > TRACE_BUF_SIZE. > > I don't see a bug here. What exactly are you trying to fix? Heh. vsnprintf() is going to put a NUL char at the end of the string even if you don't plan to use it. :P Another option would be to just print truncated output. We could use vscnprintf() and remove the off by one limit check. regards, dan carpenter diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 42a822d..ab76b7b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2160,9 +2160,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, goto out; } - len = vsnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args); - if (len > TRACE_BUF_SIZE) - goto out; + len = vscnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args); local_save_flags(flags); size = sizeof(*entry) + len + 1; @@ -2173,8 +2171,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, entry = ring_buffer_event_data(event); entry->ip = ip; - memcpy(&entry->buf, tbuffer, len); - entry->buf[len] = '\0'; + memcpy(&entry->buf, tbuffer, len + 1); if (!call_filter_check_discard(call, entry, buffer, event)) { __buffer_unlock_commit(buffer, event); ftrace_trace_stack(buffer, flags, 6, pc);