linux-kernel - Re: [PATCH v1] perf symbol: Avoid use after free

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Date:   Wed, 29 Mar 2023 07:52:29 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Leo Yan <leo.yan@...aro.org>, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf symbol: Avoid use after free

On 29/03/23 02:44, Ian Rogers wrote:
> If demangling succeeds then sym_name is set to the demangled string
> that is freed. Rather than test if sym_name is empty and possibly
> use-after-free on the return path, expand out the alternatives.

Looks the same as:

https://lore.kernel.org/linux-perf-users/20230316194156.8320-2-adrian.hunter@intel.com/

> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/symbol-elf.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index c0a2de42c51b..b7e3e492bff3 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -577,15 +577,17 @@ static bool get_plt_got_name(GElf_Shdr *shdr, size_t i,
>  	/* Get the associated symbol */
>  	gelf_getsym(di->dynsym_data, vr->sym_idx, &sym);
>  	sym_name = elf_sym__name(&sym, di->dynstr_data);
> -	demangled = demangle_sym(di->dso, 0, sym_name);
> -	if (demangled != NULL)
> -		sym_name = demangled;
> -
> -	snprintf(buf, buf_sz, "%s@plt", sym_name);
> -
> -	free(demangled);
> +	if (*sym_name == '\0')
> +		return false;
>  
> -	return *sym_name;
> +	demangled = demangle_sym(di->dso, 0, sym_name);
> +	if (demangled != NULL) {
> +		snprintf(buf, buf_sz, "%s@plt", demangled);
> +		free(demangled);
> +	} else {
> +		snprintf(buf, buf_sz, "%s@plt", sym_name);
> +	}
> +	return true;
>  }
>  
>  static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,