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Subject[PATCH 3.12 052/142] perf/core: Fix event inheritance on fork()
Date
From: Peter Zijlstra <peterz@infradead.org>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

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@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: oleg@redhat.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@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
kernel/events/core.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index a4a1516f3efc..0a360d3868c5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7754,7 +7754,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
ret = inherit_task_group(event, parent, parent_ctx,
child, ctxn, &inherited_all);
if (ret)
- break;
+ goto out_unlock;
}

/*
@@ -7770,7 +7770,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
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);
@@ -7798,6 +7798,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
}

raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+out_unlock:
mutex_unlock(&parent_ctx->mutex);

perf_unpin_context(parent_ctx);
--
2.12.2
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