linux-kernel - [PATCH 3.2 25/95] perf/core: Fix event inheritance on fork()

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Message-ID: <lsq.1500213398.931375652@decadent.org.uk>
Date:   Sun, 16 Jul 2017 14:56:38 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Arnaldo Carvalho de Melo" <acme@...nel.org>,
        "Dmitry Vyukov" <dvyukov@...gle.com>,
        "Alexander Shishkin" <alexander.shishkin@...ux.intel.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Frederic Weisbecker" <fweisbec@...il.com>,
        "Jiri Olsa" <jolsa@...hat.com>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>, oleg@...hat.com,
        "Vince Weaver" <vincent.weaver@...ne.edu>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Stephane Eranian" <eranian@...gle.com>
Subject: [PATCH 3.2 25/95] perf/core: Fix event inheritance on fork()

3.2.91-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@...radead.org>

commit e7cc4865f0f31698ef2f7aac01a50e78968985b7 upstream.

While hunting for clues to a use-after-free, Oleg spotted that
perf_event_init_context() can loose an error value with the result
that fork() can succeed even though we did not fully inherit the perf
event context.

Spotted-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: oleg@...hat.com
Fixes: 889ff0150661 ("perf/core: Split context's event group list into pinned and non-pinned lists")
Link: http://lkml.kernel.org/r/20170316125823.190342547@infradead.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/events/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7273,7 +7273,7 @@ int perf_event_init_context(struct task_
 		ret = inherit_task_group(event, parent, parent_ctx,
 					 child, ctxn, &inherited_all);
 		if (ret)
-			break;
+			goto out_unlock;
 	}
 
 	/*
@@ -7289,7 +7289,7 @@ int perf_event_init_context(struct task_
 		ret = inherit_task_group(event, parent, parent_ctx,
 					 child, ctxn, &inherited_all);
 		if (ret)
-			break;
+			goto out_unlock;
 	}
 
 	raw_spin_lock_irqsave(&parent_ctx->lock, flags);
@@ -7317,6 +7317,7 @@ int perf_event_init_context(struct task_
 	}
 
 	raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+out_unlock:
 	mutex_unlock(&parent_ctx->mutex);
 
 	perf_unpin_context(parent_ctx);