From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754152AbeDKSDg (ORCPT ); Wed, 11 Apr 2018 14:03:36 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:37060 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753116AbeDKSDc (ORCPT ); Wed, 11 Apr 2018 14:03:32 -0400 From: Song Liu To: Ingo Molnar CC: Vince Weaver , "linux-kernel@vger.kernel.org" , Peter Zijlstra Subject: Re: perf: fuzzer leads to trace_kprobe: Could not insert message flood Thread-Topic: perf: fuzzer leads to trace_kprobe: Could not insert message flood Thread-Index: AQHT0NsKF6lgcxb36UeZZJCEysMOEaP6arGAgAEOK4CAAGP5AA== Date: Wed, 11 Apr 2018 18:02:37 +0000 Message-ID: References: <20180411120447.2gzrwijrtayjv3eg@gmail.com> In-Reply-To: <20180411120447.2gzrwijrtayjv3eg@gmail.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3445.6.18) x-originating-ip: [2620:10d:c090:200::4:bb2e] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR15MB1562;7:aBXkthG3FNUB52ajGOGfivQ138d+5Gayels9WP6ybl3vUjN32dD1p/9zFBQQ6Q6pQBswA/Dlef/z6g2X0XgEzaognwyiHX3epbTQAlvueu7OuEFY6WOfXzqFjO22cp41zUf4ilNAPmCdwU48iWuGvKjFt9q1q+WvawTkKNec7sbxavg9vMYhO2lfZj0TmblPV0WGLOIaE7kRs3PBantUg7hn15lNR3qiL1d8ABH9fTRg/PmFbhqZuylGe2EAgR0G;20:Z/2cHmsUu3IugME5jvGJUPdXxBxmZ75krHcezCuYYwC/TlzJbff4AKVr0gsJVwlpWeJ1ARfaG3lMDEmPczuIo6mEIBbKt5tP3aU7xeN36RHIUr+JVlmj99cn27E3xE3x1EKndzbfFn+x+jxhFtaWps3h/V5pDJze7xXBeWe92w0= x-ms-exchange-antispam-srfa-diagnostics: SOS; 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Based on >> my limited understanding of perf_fuzzer, it doesn't understand this API, and uses >> it in an abnormal way. [...] > > Vince's point is valid: the kernel log should not be flooded with pointless > messages as a response to user-space ABI uses ... > > Why is there a kernel log message at all, isn't an error returned? > >> [...] I would recommend perf_fuzzer to understand this new API and test it. >> [...] > > This bug needs to be fixed: a new API must not effectively DoS fuzzing efforts by > spamming the kernel log ... Yeah, the new API allows non-root user to trigger this message. We should only allow root to create kprobe with perf_event_open(). On the other hand, do we need to fix this for root? In fact, a simple bash loop can create something similar through the text interface (with root): root@virt-test:~# for x in {0..5} ; do echo p:xx xx+$x >> /sys/kernel/debug/tracing/kprobe_events ; done -bash: echo: write error: No such file or directory -bash: echo: write error: No such file or directory -bash: echo: write error: No such file or directory -bash: echo: write error: No such file or directory -bash: echo: write error: No such file or directory -bash: echo: write error: No such file or directory root@virt-test:~# dmesg | tail -n 5 [ 664.208374] trace_kprobe: Could not insert probe at xx+1: -2 [ 664.237882] trace_kprobe: Could not insert probe at xx+2: -2 [ 664.268067] trace_kprobe: Could not insert probe at xx+3: -2 [ 664.297395] trace_kprobe: Could not insert probe at xx+4: -2 [ 664.327614] trace_kprobe: Could not insert probe at xx+5: -2 This happens before the new API is introduced. The following patch does capable(CAP_SYS_ADMIN) for perf_kprobe and perf_uprobe at an earlier stage, so non-root user cannot trigger this error message. Please let me know whether we need to fix this for root. Thanks, Song >>From c6708e9e3cd5ba7afb5a7f693b04abf64fec031e Mon Sep 17 00:00:00 2001 From: Song Liu Date: Wed, 11 Apr 2018 10:37:00 -0700 Subject: [PATCH] perf: need CAP_SYS_ADMIN to create k/uprobe with perf_event_open() Non-root user cannot create kprobe or uprobe through the text-based interface (kprobe_events, uprobe_events). So they cannot create the probes with perf_event_open(). To ensure this, we check capable(CAP_SYS_ADMIN) at perf_[k,u]probe_event_init(). Fixes: e12f03d7031a ("perf/core: Implement the 'perf_kprobe' PMU") Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU") Signed-off-by: Song Liu Reported-by: Vince Weaver Cc: Ingo Molnar --- kernel/events/core.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index d7af828..2d5fe26 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8400,6 +8400,10 @@ static int perf_kprobe_event_init(struct perf_event *event) if (event->attr.type != perf_kprobe.type) return -ENOENT; + + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; + /* * no branch sampling for probe events */ @@ -8437,6 +8441,10 @@ static int perf_uprobe_event_init(struct perf_event *event) if (event->attr.type != perf_uprobe.type) return -ENOENT; + + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; + /* * no branch sampling for probe events */ -- 2.9.5