Re: [PATCH v1] perf symbol-minimal: Fix double free in filename__read_build_id

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

On Thu, May 01, 2025 at 12:00:03AM -0700, Ian Rogers wrote:
> Running the "perf script task-analyzer tests" with address sanitizer
> showed a double free:
> ```
> FAIL: "test_csv_extended_times" Error message: "Failed to find required string:'Out-Out;'."
> =================================================================
> ==19190==ERROR: AddressSanitizer: attempting double-free on 0x50b000017b10 in thread T0:
>     #0 0x55da9601c78a in free (perf+0x26078a) (BuildId: e7ef50e08970f017a96fde6101c5e2491acc674a)
>     #1 0x55da96640c63 in filename__read_build_id tools/perf/util/symbol-minimal.c:221:2
> 
> 0x50b000017b10 is located 0 bytes inside of 112-byte region [0x50b000017b10,0x50b000017b80)
> freed by thread T0 here:
>     #0 0x55da9601ce40 in realloc (perf+0x260e40) (BuildId: e7ef50e08970f017a96fde6101c5e2491acc674a)
>     #1 0x55da96640ad6 in filename__read_build_id tools/perf/util/symbol-minimal.c:204:10
> 
> previously allocated by thread T0 here:
>     #0 0x55da9601ca23 in malloc (perf+0x260a23) (BuildId: e7ef50e08970f017a96fde6101c5e2491acc674a)
>     #1 0x55da966407e7 in filename__read_build_id tools/perf/util/symbol-minimal.c:181:9
> 
> SUMMARY: AddressSanitizer: double-free (perf+0x26078a) (BuildId: e7ef50e08970f017a96fde6101c5e2491acc674a) in free
> ==19190==ABORTING
> FAIL: "invocation of perf script report task-analyzer --csv-summary csvsummary --summary-extended command failed" Error message: ""
> FAIL: "test_csvsummary_extended" Error message: "Failed to find required string:'Out-Out;'."
> ---- end(-1) ----
> 132: perf script task-analyzer tests                                 : FAILED!
> ```
> 
> The buf_size if always set to phdr->p_filesz, but that may be 0
> causing a free and realloc to return NULL. This is treated in
> filename__read_build_id like a failure and the buffer is freed again.
> 
> To avoid this problem only grow buf, meaning the buf_size will never
> be 0. This also reduces the number of memory (re)allocations.

Thanks for fixing this!

Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung

> 
> Fixes: b691f64360ec ("perf symbols: Implement poor man's ELF parser")
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/symbol-minimal.c | 34 +++++++++++++++++---------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> index c6f369b5d893..d8da3da01fe6 100644
> --- a/tools/perf/util/symbol-minimal.c
> +++ b/tools/perf/util/symbol-minimal.c
> @@ -147,18 +147,19 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
>  			if (phdr->p_type != PT_NOTE)
>  				continue;
>  
> -			buf_size = phdr->p_filesz;
>  			offset = phdr->p_offset;
> -			tmp = realloc(buf, buf_size);
> -			if (tmp == NULL)
> -				goto out_free;
> -
> -			buf = tmp;
> +			if (phdr->p_filesz > buf_size) {
> +				buf_size = phdr->p_filesz;
> +				tmp = realloc(buf, buf_size);
> +				if (tmp == NULL)
> +					goto out_free;
> +				buf = tmp;
> +			}
>  			fseek(fp, offset, SEEK_SET);
> -			if (fread(buf, buf_size, 1, fp) != 1)
> +			if (fread(buf, phdr->p_filesz, 1, fp) != 1)
>  				goto out_free;
>  
> -			ret = read_build_id(buf, buf_size, bid, need_swap);
> +			ret = read_build_id(buf, phdr->p_filesz, bid, need_swap);
>  			if (ret == 0) {
>  				ret = bid->size;
>  				break;
> @@ -199,18 +200,19 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
>  			if (phdr->p_type != PT_NOTE)
>  				continue;
>  
> -			buf_size = phdr->p_filesz;
>  			offset = phdr->p_offset;
> -			tmp = realloc(buf, buf_size);
> -			if (tmp == NULL)
> -				goto out_free;
> -
> -			buf = tmp;
> +			if (phdr->p_filesz > buf_size) {
> +				buf_size = phdr->p_filesz;
> +				tmp = realloc(buf, buf_size);
> +				if (tmp == NULL)
> +					goto out_free;
> +				buf = tmp;
> +			}
>  			fseek(fp, offset, SEEK_SET);
> -			if (fread(buf, buf_size, 1, fp) != 1)
> +			if (fread(buf, phdr->p_filesz, 1, fp) != 1)
>  				goto out_free;
>  
> -			ret = read_build_id(buf, buf_size, bid, need_swap);
> +			ret = read_build_id(buf, phdr->p_filesz, bid, need_swap);
>  			if (ret == 0) {
>  				ret = bid->size;
>  				break;
> -- 
> 2.49.0.967.g6a0df3ecc3-goog
>