From ffc52b7ae5e6ff2b57c05fa8954fd4cae4efaab4 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Tue, 2 Mar 2021 02:35:33 +0000 Subject: perf diff: Don't crash on freeing errno-session on the error path __cmd_diff() sets result of perf_session__new() to d->session. In case of failure, it's errno and perf-diff may crash with: failed to open perf.data: Permission denied Failed to open perf.data Segmentation fault (core dumped) From the coredump: 0 0x00005569a62b5955 in auxtrace__free (session=0xffffffffffffffff) at util/auxtrace.c:2681 1 0x00005569a626b37d in perf_session__delete (session=0xffffffffffffffff) at util/session.c:295 2 perf_session__delete (session=0xffffffffffffffff) at util/session.c:291 3 0x00005569a618008a in __cmd_diff () at builtin-diff.c:1239 4 cmd_diff (argc=, argv=) at builtin-diff.c:2011 [..] Funny enough, it won't always crash. For me it crashes only if failed file is second in cmd-line: the reason is that cmd_diff() check files for branch-stacks [in check_file_brstack()] and if the first file doesn't have brstacks, it doesn't proceed to try open other files from cmd-line. Check d->session before calling perf_session__delete(). Another solution would be assigning to temporary variable, checking it, but I find it easier to follow with IS_ERR() check in the same function. After some time it's still obvious why the check is needed, and with temp variable it's possible to make the same mistake. Committer testing: $ perf record sleep 1 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.001 MB perf.data (8 samples) ] $ perf diff failed to open perf.data.old: No such file or directory Failed to open perf.data.old $ perf record sleep 1 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.001 MB perf.data (8 samples) ] $ perf diff # Event 'cycles:u' # # Baseline Delta Abs Shared Object Symbol # ........ ......... ................ .......................... # 0.92% +87.66% [unknown] [k] 0xffffffff8825de16 11.39% +0.04% ld-2.32.so [.] __GI___tunables_init 87.70% ld-2.32.so [.] _dl_check_map_versions $ sudo chown root:root perf.data [sudo] password for acme: $ perf diff failed to open perf.data: Permission denied Failed to open perf.data Segmentation fault (core dumped) $ After the patch: $ perf diff failed to open perf.data: Permission denied Failed to open perf.data $ Signed-off-by: Dmitry Safonov Acked-by: Namhyung Kim Tested-by: Arnaldo Carvalho de Melo Cc: Alexander Shishkin Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Jiri Olsa Cc: Mark Rutland Cc: Peter Zijlstra Cc: dmitry safonov Link: http://lore.kernel.org/lkml/20210302023533.1572231-1-dima@arista.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/builtin-diff.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'tools/perf') diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c index 8f6c784ce629..878e04b1fab7 100644 --- a/tools/perf/builtin-diff.c +++ b/tools/perf/builtin-diff.c @@ -1236,7 +1236,8 @@ static int __cmd_diff(void) out_delete: data__for_each_file(i, d) { - perf_session__delete(d->session); + if (!IS_ERR(d->session)) + perf_session__delete(d->session); data__free(d); } -- cgit v1.2.3