Patch "perf buildid: Do not assume that readlink() returns a null terminated string" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

perf buildid: Do not assume that readlink() returns a null terminated string

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-buildid-do-not-assume-that-readlink-returns-a-null-terminated-string.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Tommi Rantala <[email protected]>
Date: Wed, 22 Mar 2017 15:06:20 +0200
Subject: perf buildid: Do not assume that readlink() returns a null terminated string

From: Tommi Rantala <[email protected]>

[ Upstream commit 5a2342111c68e623e27ee7ea3d0492d8dad6bda0 ]

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.

---
 tools/perf/util/build-id.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

@@ -182,13 +182,17 @@ char *build_id_cache__origname(const cha
 	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)) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/perf-buildid-do-not-assume-that-readlink-returns-a-null-terminated-string.patch