linux-kernel - Re: [PATCH] Check jvmti_agent snprintf return value to avoid build failures with GCC-8.1.1

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Date:   Wed, 11 Jul 2018 00:58:24 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     William Cohen <wcohen@...hat.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org
Subject: Re: [PATCH] Check jvmti_agent snprintf return value to avoid build
 failures with GCC-8.1.1

On Tue, Jul 10, 2018 at 02:27:16PM -0400, William Cohen wrote:
> Newer versions of GCC perform static analysis to determine whether
> string truncation is possible with functions such as snprintf and
> provide a warning if truncation could occur.  The make for
> jvmti_agent.c uses the compiler option that treats any compiler
> warnings as compiler errors.  For GCC-8.1.1 in Fedora 28 this causes
> the build to fail.  The return value of the snprint is now checked to
> ensure snprintf produced a NULL-terminated string.  If the string for
> the path is invalid, the code does attempt to use the string.

hi,
I posted fix for this recently:
  https://lore.kernel.org/lkml/20180702134202.17745-1-jolsa@kernel.org/

it also covers the perf_regs.c, which was failing with gcc8 for me

should be pulled in soon

thanks,
jirka

> 
> Signed-off-by: William Cohen <wcohen@...hat.com>
> ---
>  tools/perf/jvmti/jvmti_agent.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/jvmti/jvmti_agent.c b/tools/perf/jvmti/jvmti_agent.c
> index 0c6d1002b524..30f14eafe4b3 100644
> --- a/tools/perf/jvmti/jvmti_agent.c
> +++ b/tools/perf/jvmti/jvmti_agent.c
> @@ -227,7 +227,7 @@ void *jvmti_open(void)
>  {
>  	char dump_path[PATH_MAX];
>  	struct jitheader header;
> -	int fd;
> +	int retlen, fd;
>  	FILE *fp;
>  
>  	init_arch_timestamp();
> @@ -249,7 +249,10 @@ void *jvmti_open(void)
>  	/*
>  	 * jitdump file name
>  	 */
> -	snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump", jit_path, getpid());
> +	retlen = snprintf(dump_path, PATH_MAX, "%s/jit-%i.dump",
> +			  jit_path, getpid());
> +	if (retlen <= 0 || ((int) sizeof(dump_path)) <= retlen)
> +		return NULL;
>  
>  	fd = open(dump_path, O_CREAT|O_TRUNC|O_RDWR, 0666);
>  	if (fd == -1)
> -- 
> 2.17.1
>