linux-kernel - Re: linux-5.7-rc1/tools/testing/selftests/resctrl/cqm_test.c:89:15: error: Buffer is accessed out of bounds

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Date:   Mon, 13 Apr 2020 09:30:38 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     David Binderman <dcb314@...mail.com>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Subject: Re: linux-5.7-rc1/tools/testing/selftests/resctrl/cqm_test.c:89:15:
 error: Buffer is accessed out of bounds

+Sai

On 4/13/2020 2:43 AM, David Binderman wrote:
> Hello there,
> 
> Source code is
> 
>    while (fgets(temp, 1024, fp)) {
> 
> but
> 
>     char *token_array[8], temp[512];
> 
> Use of compiler flag -D_FORTIFY_SOURCE=2 would have found the problem.
> For example:
> 
> # include <stdio.h>
> 
> extern void g( int);
> 
> void
> f( FILE * fp)
> {
> 	char buf[ 100];
> 
> 	while (fgets( buf, 200, fp) != 0)
> 	{
> 		g( 1);
> 	}
> }
> 
> gives
> 
> $ /home/dcb/gcc/results/bin/gcc -c -g -O2 -D_FORTIFY_SOURCE=2 apr13c.cc
> In file included from /usr/include/stdio.h:867,
>                  from apr13c.cc:2:
> In function ‘char* fgets(char*, int, FILE*)’,
>     inlined from ‘void f(FILE*)’ at apr13c.cc:11:14:
> /usr/include/bits/stdio2.h:263:26: warning: call to ‘__fgets_chk_warn’ declared with attribute warning: fgets called with bigger size than length of destination buffer [-Wattribute-warning]
> 
> I suggest switch on compiler flag -D_FORTIFY_SOURCE=2 in
> all development builds.
> 

Thank you very much for catching this David.

Sai: could you include this fix in your upcoming series of fixes? Using
the pattern of "fgets(buf, sizeof(buf), ...)" instead of hard coding the
size should be helpful here.

Reinette