linux-kernel - Re: [patch] perf report segfault with 0-sized strings

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Date:   Fri, 26 Jul 2019 16:09:53 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [patch] perf report segfault with 0-sized strings

Em Thu, Jul 25, 2019 at 02:27:14PM -0400, Vince Weaver escreveu:
> Hello,
> 
> the perf_data_fuzzer found an issue when strings have size 0.
> malloc() in do_read_string() is happy to allocate a string of 
> size 0 but when code (in this case the pmu parser) tries to work with 
> those it will segfault.

So here are two fixes, i.e. one is to make do_read_string() to return
NULL when len is 0, which do_read_string() already returns for failure
(NULL) and most of the callers I looked handle that.

The other is to make print_pmu_mappings() deal with a NULL
ff->ph->env.pmu_mappings, agreed?

- Arnaldo
 
> Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index c24db7f4909c..641129efa987 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -251,6 +252,9 @@ static char *do_read_string(struct feat_fd *ff)
>  	if (do_read_u32(ff, &len))
>  		return NULL;
>  
> +	if (len==0)
> +		return NULL;
> +
>  	buf = malloc(len);
>  	if (!buf)
>  		return NULL;
> @@ -1781,6 +1785,10 @@ static void print_pmu_mappings(struct feat_fd *ff, FILE *fp)
>  	str = ff->ph->env.pmu_mappings;
>  
>  	while (pmu_num) {
> +
> +		if (str==NULL)
> +			goto error;
> +
>  		type = strtoul(str, &tmp, 0);
>  		if (*tmp != ':')
>  			goto error;

-- 

- Arnaldo