From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755246AbcKYPNR (ORCPT ); Fri, 25 Nov 2016 10:13:17 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:35283 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755188AbcKYPM7 (ORCPT ); Fri, 25 Nov 2016 10:12:59 -0500 From: Arnaldo Carvalho de Melo To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Wang Nan , Alexei Starovoitov , He Kuang , Zefan Li , pi3orama@163.com, Arnaldo Carvalho de Melo Subject: [PATCH 10/12] perf record: Fix segfault when running with suid and kptr_restrict is 1 Date: Fri, 25 Nov 2016 12:12:25 -0300 Message-Id: <1480086747-2393-11-git-send-email-acme@kernel.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1480086747-2393-1-git-send-email-acme@kernel.org> References: <1480086747-2393-1-git-send-email-acme@kernel.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wang Nan Before this patch perf panics if kptr_restrict is set to 1 and perf is owned by root with suid set: $ whoami wangnan $ ls -l ./perf -rwsr-xr-x 1 root root 19781908 Sep 21 19:29 /home/wangnan/perf $ cat /proc/sys/kernel/kptr_restrict 1 $ cat /proc/sys/kernel/perf_event_paranoid -1 $ ./perf record -a Segmentation fault (core dumped) $ The reason is that perf assumes it is allowed to read kptr from /proc/kallsyms when euid is root, but in fact the kernel doesn't allow reading kptr when euid and uid do not match with each other: $ cp /bin/cat . $ sudo chown root:root ./cat $ sudo chmod u+s ./cat $ cat /proc/kallsyms | grep do_fork 0000000000000000 T _do_fork <--- kptr is hidden even euid is root $ sudo cat /proc/kallsyms | grep do_fork ffffffff81080230 T _do_fork See lib/vsprintf.c for kernel side code. This patch fixes this problem by checking both uid and euid. Signed-off-by: Wang Nan Tested-by: Arnaldo Carvalho de Melo Cc: Alexei Starovoitov Cc: He Kuang Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/20161115040617.69788-3-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/symbol.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index aecff69a510d..420ada9de22f 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -1962,7 +1962,7 @@ static bool symbol__read_kptr_restrict(void) char line[8]; if (fgets(line, sizeof(line), fp) != NULL) - value = (geteuid() != 0) ? + value = ((geteuid() != 0) || (getuid() != 0)) ? (atoi(line) != 0) : (atoi(line) == 2); -- 2.7.4