linux-kernel - [PATCH 5.4 037/222] perf: Correctly handle failed perf_get_aux

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Message-Id: <20200122092836.175504422@linuxfoundation.org>
Date:   Wed, 22 Jan 2020 10:27:03 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vince Weaver <vincent.weaver@...ne.edu>,
        Mark Rutland <mark.rutland@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: [PATCH 5.4 037/222] perf: Correctly handle failed perf_get_aux_event()

From: Mark Rutland <mark.rutland@....com>

commit da9ec3d3dd0f1240a48920be063448a2242dbd90 upstream.

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Tested-by: Vince Weaver <vincent.weaver@...ne.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/events/core.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11182,8 +11182,10 @@ SYSCALL_DEFINE5(perf_event_open,
 		}
 	}
 
-	if (event->attr.aux_output && !perf_get_aux_event(event, group_leader))
+	if (event->attr.aux_output && !perf_get_aux_event(event, group_leader)) {
+		err = -EINVAL;
 		goto err_locked;
+	}
 
 	/*
 	 * Must be under the same ctx::mutex as perf_install_in_context(),