linux-kernel - [tip: perf/urgent] perf: Correctly handle failed perf_get_aux

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Date:   Fri, 17 Jan 2020 10:08:39 -0000
From:   "tip-bot2 for Mark Rutland" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: perf/urgent] perf: Correctly handle failed perf_get_aux_event()

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     2bef101686951c743a6c98ca68cc3b3193f1fb81
Gitweb:        https://git.kernel.org/tip/2bef101686951c743a6c98ca68cc3b3193f1fb81
Author:        Mark Rutland <mark.rutland@....com>
AuthorDate:    Mon, 06 Jan 2020 12:03:39 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 17 Jan 2020 10:19:24 +01:00

perf: Correctly handle failed perf_get_aux_event()

Vince reports a worrying issue:

| so I was tracking down some odd behavior in the perf_fuzzer which turns
| out to be because perf_even_open() sometimes returns 0 (indicating a file
| descriptor of 0) even though as far as I can tell stdin is still open.

... and further the cause:

| error is triggered if aux_sample_size has non-zero value.
|
| seems to be this line in kernel/events/core.c:
|
| if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader))
|                goto err_locked;
|
| (note, err is never set)

This seems to be a thinko in commit:

  ab43762ef010967e ("perf: Allow normal events to output AUX data")

... and we should probably return -EINVAL here, as this should only
happen when the new event is mis-configured or does not have a
compatible aux_event group leader.

Fixes: ab43762ef010967e ("perf: Allow normal events to output AUX data")
Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Acked-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Tested-by: Vince Weaver <vincent.weaver@...ne.edu>
---
 kernel/events/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index a1f8bde..2173c23 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11465,8 +11465,10 @@ SYSCALL_DEFINE5(perf_event_open,
 		}
 	}

-	if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader))
+	if (perf_need_aux_event(event) && !perf_get_aux_event(event, group_leader)) {
+		err = -EINVAL;
 		goto err_locked;
+	}

 	/*
 	 * Must be under the same ctx::mutex as perf_install_in_context(),