[PATCH 2/6] perf buildid: do not assume that readlink() returns a null terminated string

From: Tommi Rantala
Date: Wed Mar 22 2017 - 09:09:43 EST


Valgrind was complaining:

$ valgrind ./perf list >/dev/null
==11643== Memcheck, a memory error detector
==11643== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==11643== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==11643== Command: ./perf list
==11643==
==11643== Conditional jump or move depends on uninitialised value(s)
==11643== at 0x4C30620: rindex (vg_replace_strmem.c:199)
==11643== by 0x49DAA9: build_id_cache__origname (build-id.c:198)
==11643== by 0x49E1C7: build_id_cache__valid_id (build-id.c:222)
==11643== by 0x49E1C7: build_id_cache__list_all (build-id.c:507)
==11643== by 0x4B9C8F: print_sdt_events (parse-events.c:2067)
==11643== by 0x4BB0B3: print_events (parse-events.c:2313)
==11643== by 0x439501: cmd_list (builtin-list.c:53)
==11643== by 0x497150: run_builtin (perf.c:359)
==11643== by 0x428CE0: handle_internal_command (perf.c:421)
==11643== by 0x428CE0: run_argv (perf.c:467)
==11643== by 0x428CE0: main (perf.c:614)
[...]

Additionally, a zero length result from readlink() is not very interesting.

Signed-off-by: Tommi Rantala <tommi.t.rantala@xxxxxxxxx>
---
tools/perf/util/build-id.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index 234859f..9ad77b0 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -182,13 +182,17 @@ char *build_id_cache__origname(const char *sbuild_id)
char buf[PATH_MAX];
char *ret = NULL, *p;
size_t offs = 5; /* == strlen("../..") */
+ ssize_t len;

linkname = build_id_cache__linkname(sbuild_id, NULL, 0);
if (!linkname)
return NULL;

- if (readlink(linkname, buf, PATH_MAX) < 0)
+ len = readlink(linkname, buf, sizeof(buf)-1);
+ if (len <= 0)
goto out;
+ buf[len] = '\0';
+
/* The link should be "../..<origpath>/<sbuild_id>" */
p = strrchr(buf, '/'); /* Cut off the "/<sbuild_id>" */
if (p && (p > buf + offs)) {
--
2.9.3