linux-kernel - [PATCH 16/20] perf buildid: Do not assume that readlink() returns a null terminated string

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Message-Id: <20170328013915.15236-17-acme@kernel.org>
Date:   Mon, 27 Mar 2017 22:39:11 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Tommi Rantala <tommi.t.rantala@...ia.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 16/20] perf buildid: Do not assume that readlink() returns a null terminated string

From: Tommi Rantala <tommi.t.rantala@...ia.com>

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@...ia.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/20170322130624.21881-3-tommi.t.rantala@nokia.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 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 234859f756c4..33af67530d30 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