[PATCH] perf: fix alloc_callchain_buffers()

* [PATCH] perf: fix alloc_callchain_buffers()
@ 2011-01-25 18:40 Eric Dumazet
  2011-01-26  7:25 ` [tip:perf/urgent] perf: Fix alloc_callchain_buffers() tip-bot for Eric Dumazet
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Eric Dumazet @ 2011-01-25 18:40 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Frederic Weisbecker, stable, Peter Zijlstra,
	Arnaldo Carvalho de Melo, David Miller, Stephane Eranian

Commit 927c7a9e92c4 ( perf: Fix race in callchains ) introduced a
mismatch in the sizing of struct callchain_cpus_entries.

nr_cpu_ids must be used instead of num_possible_cpus(), or we might get
out of bound memory accesses on some machines.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Arnaldo Carvalho de Melo <acme@redhat.com>
CC: David Miller <davem@davemloft.net>
CC: Stephane Eranian <eranian@google.com>
CC: stable@kernel.org
---
 kernel/perf_event.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 126a302..852ae8c 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1999,8 +1999,7 @@ static int alloc_callchain_buffers(void)
 	 * accessed from NMI. Use a temporary manual per cpu allocation
 	 * until that gets sorted out.
 	 */
-	size = sizeof(*entries) + sizeof(struct perf_callchain_entry *) *
-		num_possible_cpus();
+	size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
 
 	entries = kzalloc(size, GFP_KERNEL);
 	if (!entries)



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