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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Tommi Rantala <tommi.t.rantala@nokia.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 071/219] perf buildid: Do not assume that
 readlink() returns a null terminated string
Thread-Topic: [PATCH AUTOSEL for 4.9 071/219] perf buildid: Do not assume that
 readlink() returns a null terminated string
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Date:   Sat, 3 Mar 2018 22:28:37 +0000
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From: Tommi Rantala <tommi.t.rantala@nokia.com>

[ Upstream commit 5a2342111c68e623e27ee7ea3d0492d8dad6bda0 ]

Valgrind was complaining:

  $ valgrind ./perf list >/dev/null
  =3D=3D11643=3D=3D Memcheck, a memory error detector
  =3D=3D11643=3D=3D Copyright (C) 2002-2015, and GNU GPL'd, by Julian Sewar=
d et al.
  =3D=3D11643=3D=3D Using Valgrind-3.12.0 and LibVEX; rerun with -h for cop=
yright info
  =3D=3D11643=3D=3D Command: ./perf list
  =3D=3D11643=3D=3D
  =3D=3D11643=3D=3D Conditional jump or move depends on uninitialised value=
(s)
  =3D=3D11643=3D=3D    at 0x4C30620: rindex (vg_replace_strmem.c:199)
  =3D=3D11643=3D=3D    by 0x49DAA9: build_id_cache__origname (build-id.c:19=
8)
  =3D=3D11643=3D=3D    by 0x49E1C7: build_id_cache__valid_id (build-id.c:22=
2)
  =3D=3D11643=3D=3D    by 0x49E1C7: build_id_cache__list_all (build-id.c:50=
7)
  =3D=3D11643=3D=3D    by 0x4B9C8F: print_sdt_events (parse-events.c:2067)
  =3D=3D11643=3D=3D    by 0x4BB0B3: print_events (parse-events.c:2313)
  =3D=3D11643=3D=3D    by 0x439501: cmd_list (builtin-list.c:53)
  =3D=3D11643=3D=3D    by 0x497150: run_builtin (perf.c:359)
  =3D=3D11643=3D=3D    by 0x428CE0: handle_internal_command (perf.c:421)
  =3D=3D11643=3D=3D    by 0x428CE0: run_argv (perf.c:467)
  =3D=3D11643=3D=3D    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@nokia.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170322130624.21881-3-tommi.t.rantala@nokia=
.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.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 e528c40739cc..993ef2762508 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 =3D NULL, *p;
 	size_t offs =3D 5;	/* =3D=3D strlen("../..") */
+	ssize_t len;
=20
 	linkname =3D build_id_cache__linkname(sbuild_id, NULL, 0);
 	if (!linkname)
 		return NULL;
=20
-	if (readlink(linkname, buf, PATH_MAX) < 0)
+	len =3D readlink(linkname, buf, sizeof(buf) - 1);
+	if (len <=3D 0)
 		goto out;
+	buf[len] =3D '\0';
+
 	/* The link should be "../..<origpath>/<sbuild_id>" */
 	p =3D strrchr(buf, '/');	/* Cut off the "/<sbuild_id>" */
 	if (p && (p > buf + offs)) {
--=20
2.14.1