linux-kernel - Re: [PATCH v2] trace-cmd: prevent print_graph

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Date:	Tue, 15 Jun 2010 10:54:21 -0400
From:	Steven Rostedt <srostedt@...hat.com>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	Valdis.Kletnieks@...edu, Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] trace-cmd: prevent print_graph_duration buffer
 overflow

Quick note. Please send to my rostedt@...dmis.org address. I may not see
messages here for weeks at a time. I author patches with my RH account
just to "advertise" who I work for. But I sign-off-by with the account I
want people to send to.


On Tue, 2010-06-15 at 10:47 -0400, Chase Douglas wrote:
> Passing n > sizeof(string) to snprintf can cause a glibc buffer overflow
> condition. We know the exact size of nsecs_str, so use it along with the
> the math to determine the longest string size we want.
> 
> Note that an overflow isn't really possible given the format of the
> string. However, glibc would abort due to a runtime check.
> 
> Signed-off-by: Chase Douglas <chase.douglas@...onical.com>

Thanks!

Can you write a similar patch for the Linux kernel too. It may need to
go to stable as well.

-- Steve

> ---
>  trace-ftrace.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/trace-ftrace.c b/trace-ftrace.c
> index af9ac8d..181a00f 100644
> --- a/trace-ftrace.c
> +++ b/trace-ftrace.c
> @@ -21,6 +21,7 @@
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
> +#include <sys/param.h>
>  
>  #include "trace-cmd.h"
>  
> @@ -148,7 +149,7 @@ static void print_graph_duration(struct trace_seq *s, unsigned long long duratio
>  
>  	/* Print nsecs (we don't want to exceed 7 numbers) */
>  	if ((s->len - len) < 7) {
> -		snprintf(nsecs_str, 8 - (s->len - len), "%03lu", nsecs_rem);
> +		snprintf(nsecs_str, MIN(sizeof(nsecs_str), 8 - len), "%03lu", nsecs_rem);
>  		trace_seq_printf(s, ".%s", nsecs_str);
>  	}
>  

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