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SubjectRe: [PATCH v2] Fix annotate.c use of uninitialized value error
On Mon, Jul 29, 2019 at 01:57:50PM -0700, Numfor Mbiziwo-Tiapo wrote:
> Our local MSAN (Memory Sanitizer) build of perf throws a warning
> that comes from the "dso__disassemble_filename" function in
> "tools/perf/util/annotate.c" when running perf record.
>
> The warning stems from the call to readlink, in which "build_id_path"
> was being read into "linkname". Since readlink does not null terminate,
> an uninitialized memory access would later occur when "linkname" is
> passed into the strstr function. This is simply fixed by null-terminating
> "linkname" after the call to readlink.
>
> To reproduce this warning, build perf by running:
> make -C tools/perf CLANG=1 CC=clang EXTRA_CFLAGS="-fsanitize=memory\
> -fsanitize-memory-track-origins"
>
> (Additionally, llvm might have to be installed and clang might have to
> be specified as the compiler - export CC=/usr/bin/clang)
>
> then running:
> tools/perf/perf record -o - ls / | tools/perf/perf --no-pager annotate\
> -i - --stdio
>
> Please see the cover letter for why false positive warnings may be
> generated.
>
> Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> ---
> tools/perf/util/annotate.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index 70de8f6b3aee..e1b075b52dce 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -1627,6 +1627,7 @@ static int dso__disassemble_filename(struct dso *dso, char *filename, size_t fil
> char *build_id_filename;
> char *build_id_path = NULL;
> char *pos;
> + int len;
>
> if (dso->symtab_type == DSO_BINARY_TYPE__KALLSYMS &&
> !dso__is_kcore(dso))
> @@ -1655,10 +1656,16 @@ static int dso__disassemble_filename(struct dso *dso, char *filename, size_t fil
> if (pos && strlen(pos) < SBUILD_ID_SIZE - 2)
> dirname(build_id_path);
>
> - if (dso__is_kcore(dso) ||
> - readlink(build_id_path, linkname, sizeof(linkname)) < 0 ||
> - strstr(linkname, DSO__NAME_KALLSYMS) ||
> - access(filename, R_OK)) {
> + if (dso__is_kcore(dso))
> + goto fallback;
> +
> + len = readlink(build_id_path, linkname, sizeof(linkname) - 1);
> + if (len < 0)
> + goto fallback;
> +
> + linkname[len] = '\0';
> + if (strstr(linkname, DSO__NAME_KALLSYMS) ||
> + access(filename, R_OK)) {
> fallback:
> /*
> * If we don't have build-ids or the build-id file isn't in the
> --
> 2.22.0.709.g102302147b-goog
>

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