Re: [PATCH] perf tools: Fix crash in build_id_cache__kallsyms_path()

[Masami Hiramatsu <mhiramat@kernel.org>]

On Tue, 7 Jun 2016 03:54:38 +0000
Wang Nan <wangnan0@huawei.com> wrote:

> build_id_cache__kallsyms_path() accept string buffer but also alloc buffer
> by itself using asnprintf. Unfortunately, the only user of it passes it
> a stack-allocated buffer. Freeing it causes crash like this:
> 
>  $ perf script
>  *** Error in `/home/wangnan/perf': free(): invalid pointer: 0x00007fffffff9630 ***
>  ======= Backtrace: =========
>  lib64/libc.so.6(+0x6eeef)[0x7ffff5dbaeef]
>  lib64/libc.so.6(+0x78cae)[0x7ffff5dc4cae]
>  lib64/libc.so.6(+0x79987)[0x7ffff5dc5987]
>  /home/w00229757/perf(build_id_cache__kallsyms_path+0x6b)[0x49681b]
>  /home/w00229757/perf[0x4bdd40]
>  /home/w00229757/perf(dso__load+0xa3a)[0x4c048a]
>  /home/w00229757/perf(map__load+0x6f)[0x4d561f]
>  /home/w00229757/perf(thread__find_addr_map+0x235)[0x49e935]
>  /home/w00229757/perf(machine__resolve+0x7d)[0x49ec6d]
>  /home/w00229757/perf[0x4555a8]
>  /home/w00229757/perf[0x4d9507]
>  /home/w00229757/perf[0x4d9e80]
>  /home/w00229757/perf(ordered_events__flush+0x354)[0x4dd444]
>  /home/w00229757/perf(perf_session__process_events+0x3d0)[0x4dc140]
>  /home/w00229757/perf(cmd_script+0x12b0)[0x4592e0]
>  /home/w00229757/perf[0x4911f1]
>  /home/w00229757/perf(main+0x68f)[0x4352ef]
>  /lib64/libc.so.6(__libc_start_main+0xf5)[0x7ffff5d6dbd5]
>  /home/w00229757/perf[0x435415]
>  ======= Memory map: ========
> 
> This patch simplify build_id_cache__kallsyms_path(), don't even consider
> allocate string buffer, so never free anything. The caller of it should
> management memory allocation.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Fixes: 01412261d994 ("perf buildid-cache: Use path/to/bin/buildid/elf instead of path/to/bin/buildid")
> ---
>  tools/perf/util/build-id.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
> index 67f986c..20aef90 100644
> --- a/tools/perf/util/build-id.c
> +++ b/tools/perf/util/build-id.c
> @@ -147,20 +147,17 @@ static int asnprintf(char **strp, size_t size, const char *fmt, ...)
>  char *build_id_cache__kallsyms_path(const char *sbuild_id, char *bf,
>  				    size_t size)
>  {
> -	bool is_alloc = !!bf;

Oops, I think this is the reason why it failed.
is_alloc should be !bf (means allocation needed)

>  	bool retry_old = true;
>  
> -	asnprintf(&bf, size, "%s/%s/%s/kallsyms",
> -		  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
> +	snprintf(bf, size, "%s/%s/%s/kallsyms",
> +		 buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
>  retry:
>  	if (!access(bf, F_OK))
>  		return bf;
> -	if (is_alloc)
> -		free(bf);

Then, it works well.

Thanks,

>  	if (retry_old) {
>  		/* Try old style kallsyms cache */
> -		asnprintf(&bf, size, "%s/%s/%s",
> -			  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
> +		snprintf(bf, size, "%s/%s/%s",
> +			 buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
>  		retry_old = false;
>  		goto retry;
>  	}
> -- 
> 1.8.3.4
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>