linux-kernel - Re: [PATCH v4 11/17] selftests/resctrl: Enable gcc checks to detect buffer overflows

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Date:   Mon, 25 Jan 2021 19:38:54 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Fenghua Yu <fenghua.yu@...el.com>, Shuah Khan <shuah@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        David Binderman <dcb314@...mail.com>,
        Babu Moger <babu.moger@....com>,
        James Morse <james.morse@....com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 11/17] selftests/resctrl: Enable gcc checks to detect
 buffer overflows

On 11/30/20 1:20 PM, Fenghua Yu wrote:
> David reported a buffer overflow error in the check_results() function of
> the cmt unit test and he suggested enabling _FORTIFY_SOURCE gcc compiler
> option to automatically detect any such errors.
> 
> Feature Test Macros man page describes_FORTIFY_SOURCE as below
> 
> "Defining this macro causes some lightweight checks to be performed to
> detect some buffer overflow errors when employing various string and memory
> manipulation functions (for example, memcpy, memset, stpcpy, strcpy,
> strncpy, strcat, strncat, sprintf, snprintf, vsprintf, vsnprintf, gets, and
> wide character variants thereof). For some functions, argument consistency
> is checked; for example, a check is made that open has been supplied with a
> mode argument when the specified flags include O_CREAT. Not all problems
> are detected, just some common cases.
> 
> If _FORTIFY_SOURCE is set to 1, with compiler optimization level 1 (gcc
> -O1) and above, checks that shouldn't change the behavior of conforming
> programs are performed.
> 
> With _FORTIFY_SOURCE set to 2, some more checking is added, but some
> conforming programs might fail.
> 
> Some of the checks can be performed at compile time (via macros logic
> implemented in header files), and result in compiler warnings; other checks
> take place at run time, and result in a run-time error if the check fails.
> 
> Use of this macro requires compiler support, available with gcc since
> version 4.0."
> 
> Fix the buffer overflow error in the check_results() function of the cmt
> unit test and enable _FORTIFY_SOURCE gcc check to catch any future buffer
> overflow errors.
> 
> Reported-by: David Binderman <dcb314@...mail.com>
> Suggested-by: David Binderman <dcb314@...mail.com>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>   tools/testing/selftests/resctrl/Makefile   | 2 +-
>   tools/testing/selftests/resctrl/cmt_test.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/Makefile b/tools/testing/selftests/resctrl/Makefile
> index d585cc1948cc..6bcee2ec91a9 100644
> --- a/tools/testing/selftests/resctrl/Makefile
> +++ b/tools/testing/selftests/resctrl/Makefile
> @@ -1,5 +1,5 @@
>   CC = $(CROSS_COMPILE)gcc
> -CFLAGS = -g -Wall
> +CFLAGS = -g -Wall -O2 -D_FORTIFY_SOURCE=2
>   SRCS=$(wildcard *.c)
>   OBJS=$(SRCS:.c=.o)
>   
> diff --git a/tools/testing/selftests/resctrl/cmt_test.c b/tools/testing/selftests/resctrl/cmt_test.c
> index 188b73b5a2cc..ac1a33d9ce12 100644
> --- a/tools/testing/selftests/resctrl/cmt_test.c
> +++ b/tools/testing/selftests/resctrl/cmt_test.c
> @@ -81,7 +81,7 @@ static int check_results(struct resctrl_val_param *param, int no_of_bits)
>   		return errno;
>   	}
>   
> -	while (fgets(temp, 1024, fp)) {
> +	while (fgets(temp, sizeof(temp), fp)) {
>   		char *token = strtok(temp, ":\t");
>   		int fields = 0;
>   
> 

This should be fixed first before the other changes.

thanks,
-- Shuah