linux-kernel - Re: [kees:format-security 2/3] arch/sh/kernel/dumpstack.c:118:2: error: format not a string literal and no format arguments

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Message-ID: <20140311095910.GA5834@console-pimps.org>
Date:	Tue, 11 Mar 2014 09:59:10 +0000
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	kbuild test robot <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [kees:format-security 2/3] arch/sh/kernel/dumpstack.c:118:2:
 error: format not a string literal and no format arguments

On Mon, 10 Mar, at 10:41:57AM, Kees Cook wrote:
> > 4e14dfc7 Matt Fleming 2009-08-07  113  /*
> > 4e14dfc7 Matt Fleming 2009-08-07  114   * Print one address/symbol entries per line.
> > 4e14dfc7 Matt Fleming 2009-08-07  115   */
> > 4e14dfc7 Matt Fleming 2009-08-07  116  static void print_trace_address(void *data, unsigned long addr, int reliable)
> > 4e14dfc7 Matt Fleming 2009-08-07  117  {
> > 4e14dfc7 Matt Fleming 2009-08-07 @118   printk(data);
> 
> This needs to be "printk("%s", data);" so there is no chance of having
> "data" interpreted as a format string itself.

OMG, I suck. Thanks for the report Kees. Have you got a patch for x86?
I think that's where this code came from.

Including Andrew, because I'm not sure who else is going to take this
patch.

---

>From 2284f3a27f68cec665aa982c0a226cf3fbf96ddf Mon Sep 17 00:00:00 2001
From: Matt Fleming <matt.fleming@...el.com>
Date: Tue, 11 Mar 2014 09:50:26 +0000
Subject: [PATCH] sh: Fix format string bug in stack tracer

Kees reported the following error,

   arch/sh/kernel/dumpstack.c: In function 'print_trace_address':
>> arch/sh/kernel/dumpstack.c:118:2: error: format not a string literal and no format arguments [-Werror=format-security]

Use the "%s" format so that it's impossible to interpret 'data' as a
format string.

Reported-by: Kees Cook <keescook@...omium.org>
Cc: Paul Mundt <lethal@...ux-sh.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: stable@...r.kernel.org
Signed-off-by: Matt Fleming <matt.fleming@...el.com>
---
 arch/sh/kernel/dumpstack.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/sh/kernel/dumpstack.c b/arch/sh/kernel/dumpstack.c
index b959f5592604..8dfe645bcc4b 100644
--- a/arch/sh/kernel/dumpstack.c
+++ b/arch/sh/kernel/dumpstack.c
@@ -115,7 +115,7 @@ static int print_trace_stack(void *data, char *name)
  */
 static void print_trace_address(void *data, unsigned long addr, int reliable)
 {
-	printk(data);
+	printk("%s", (char *)data);
 	printk_address(addr, reliable);
 }
 
-- 
1.8.5.3

-- 
Matt Fleming, Intel Open Source Technology Center
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