linux-kernel - [PATCH] perf tools: Fix crash in build_id_cache__kallsyms

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Date:	Tue, 7 Jun 2016 03:54:38 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<acme@...nel.org>, <mhiramat@...nel.org>
CC:	<pi3orama@....com>, <lizefan@...wei.com>,
	<linux-kernel@...r.kernel.org>, Wang Nan <wangnan0@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH] perf tools: Fix crash in build_id_cache__kallsyms_path()

build_id_cache__kallsyms_path() accept string buffer but also alloc buffer
by itself using asnprintf. Unfortunately, the only user of it passes it
a stack-allocated buffer. Freeing it causes crash like this:

 $ perf script
 *** Error in `/home/wangnan/perf': free(): invalid pointer: 0x00007fffffff9630 ***
 ======= Backtrace: =========
 lib64/libc.so.6(+0x6eeef)[0x7ffff5dbaeef]
 lib64/libc.so.6(+0x78cae)[0x7ffff5dc4cae]
 lib64/libc.so.6(+0x79987)[0x7ffff5dc5987]
 /home/w00229757/perf(build_id_cache__kallsyms_path+0x6b)[0x49681b]
 /home/w00229757/perf[0x4bdd40]
 /home/w00229757/perf(dso__load+0xa3a)[0x4c048a]
 /home/w00229757/perf(map__load+0x6f)[0x4d561f]
 /home/w00229757/perf(thread__find_addr_map+0x235)[0x49e935]
 /home/w00229757/perf(machine__resolve+0x7d)[0x49ec6d]
 /home/w00229757/perf[0x4555a8]
 /home/w00229757/perf[0x4d9507]
 /home/w00229757/perf[0x4d9e80]
 /home/w00229757/perf(ordered_events__flush+0x354)[0x4dd444]
 /home/w00229757/perf(perf_session__process_events+0x3d0)[0x4dc140]
 /home/w00229757/perf(cmd_script+0x12b0)[0x4592e0]
 /home/w00229757/perf[0x4911f1]
 /home/w00229757/perf(main+0x68f)[0x4352ef]
 /lib64/libc.so.6(__libc_start_main+0xf5)[0x7ffff5d6dbd5]
 /home/w00229757/perf[0x435415]
 ======= Memory map: ========

This patch simplify build_id_cache__kallsyms_path(), don't even consider
allocate string buffer, so never free anything. The caller of it should
management memory allocation.

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Fixes: 01412261d994 ("perf buildid-cache: Use path/to/bin/buildid/elf instead of path/to/bin/buildid")
---
 tools/perf/util/build-id.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index 67f986c..20aef90 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -147,20 +147,17 @@ static int asnprintf(char **strp, size_t size, const char *fmt, ...)
 char *build_id_cache__kallsyms_path(const char *sbuild_id, char *bf,
 				    size_t size)
 {
-	bool is_alloc = !!bf;
 	bool retry_old = true;
 
-	asnprintf(&bf, size, "%s/%s/%s/kallsyms",
-		  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
+	snprintf(bf, size, "%s/%s/%s/kallsyms",
+		 buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
 retry:
 	if (!access(bf, F_OK))
 		return bf;
-	if (is_alloc)
-		free(bf);
 	if (retry_old) {
 		/* Try old style kallsyms cache */
-		asnprintf(&bf, size, "%s/%s/%s",
-			  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
+		snprintf(bf, size, "%s/%s/%s",
+			 buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
 		retry_old = false;
 		goto retry;
 	}
-- 
1.8.3.4