[PATCH v2 23/26] perf header: Avoid out-of-bounds read

[Ian Rogers]

intel-pt tests were failing:
```
...
--- Test virtual LBR ---
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.126 MB /tmp/perf-test-intel-pt-sh.FW57CXnCqQ/test-perf.data ]
Failed with virtual lbr
...
```

The root cause is an out-of-bounds read in header (where maxbrstack.py
is from test_intel_pt.sh):
```
$ perf --no-pager script --itrace=L -s maxbrstack.py
=================================================================
==3907930==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6020000095a8 at pc 0x563c26c840bb bp 0x7fff43582710 sp 0x7fff43582708
READ of size 4 at 0x6020000095a8 thread T0
    #0 0x563c26c840ba in process_group_desc util/header.c:2847
    #1 0x563c26c8bc78 in perf_file_section__process util/header.c:4037
    #2 0x563c26c8aa9b in perf_header__process_sections util/header.c:3813
    #3 0x563c26c8d028 in perf_session__read_header util/header.c:4286
    #4 0x563c26cbab29 in perf_session__open util/session.c:113
    #5 0x563c26cbb3d0 in __perf_session__new util/session.c:221
    #6 0x563c26aacb14 in perf_session__new util/session.h:73
    #7 0x563c26acf7f1 in cmd_script tools/perf/builtin-script.c:4212
    #8 0x563c26bb58ff in run_builtin tools/perf/perf.c:323
    #9 0x563c26bb5e70 in handle_internal_command tools/perf/perf.c:377
    #10 0x563c26bb6238 in run_argv tools/perf/perf.c:421
    #11 0x563c26bb67a0 in main tools/perf/perf.c:537
    #12 0x7f34bde46189 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #13 0x7f34bde46244 in __libc_start_main_impl ../csu/libc-start.c:381
    #14 0x563c26a33390 in _start (/tmp/perf/perf+0x1eb390)

0x6020000095a8 is located 8 bytes to the right of 16-byte region [0x602000009590,0x6020000095a0)
allocated by thread T0 here:
    #0 0x7f34beeb83b7 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77
    #1 0x563c26c83df8 in process_group_desc util/header.c:2824
    #2 0x563c26c8bc78 in perf_file_section__process util/header.c:4037
    #3 0x563c26c8aa9b in perf_header__process_sections util/header.c:3813
    #4 0x563c26c8d028 in perf_session__read_header util/header.c:4286
    #5 0x563c26cbab29 in perf_session__open util/session.c:113
    #6 0x563c26cbb3d0 in __perf_session__new util/session.c:221
    #7 0x563c26aacb14 in perf_session__new util/session.h:73
    #8 0x563c26acf7f1 in cmd_script tools/perf/builtin-script.c:4212
    #9 0x563c26bb58ff in run_builtin tools/perf/perf.c:323
    #10 0x563c26bb5e70 in handle_internal_command tools/perf/perf.c:377
    #11 0x563c26bb6238 in run_argv tools/perf/perf.c:421
    #12 0x563c26bb67a0 in main tools/perf/perf.c:537
    #13 0x7f34bde46189 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
```

Avoid the out-of-bounds read checking for the leader. Leave the 'nr'
check intact as nr will be 0 or the counting down and evsel be a group
member.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/header.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 3db7c1fae71e..52fbf526fe74 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -2844,7 +2844,7 @@ static int process_group_desc(struct feat_fd *ff, void *data __maybe_unused)
 
 	i = nr = 0;
 	evlist__for_each_entry(session->evlist, evsel) {
-		if (evsel->core.idx == (int) desc[i].leader_idx) {
+		if (i < nr_groups && evsel->core.idx == (int) desc[i].leader_idx) {
 			evsel__set_leader(evsel, evsel);
 			/* {anon_group} is a dummy name */
 			if (strcmp(desc[i].name, "{anon_group}")) {
-- 
2.41.0.162.gfafddb0af9-goog