[PATCH 2/2] perf: validate cpu early in perf_event_alloc()

[Oleg Nesterov]

Starting from perf_event_alloc()->perf_init_event(), the kernel
assumes that event->cpu is either -1 or the valid CPU number.

Change perf_event_alloc() to validate this argument early. This
also means we can remove the similar check in find_get_context().

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---

 kernel/perf_event.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- git/kernel/perf_event.c~2_perf_event_alloc	2011-01-18 16:56:40.000000000 +0100
+++ git/kernel/perf_event.c	2011-01-18 16:57:08.000000000 +0100
@@ -2233,9 +2233,6 @@ find_get_context(struct pmu *pmu, struct
 		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
 			return ERR_PTR(-EACCES);
 
-		if (cpu < 0 || cpu >= nr_cpumask_bits)
-			return ERR_PTR(-EINVAL);
-
 		/*
 		 * We could be clever and allow to attach a event to an
 		 * offline CPU and activate it when the CPU comes up, but
@@ -5541,6 +5538,11 @@ perf_event_alloc(struct perf_event_attr 
 	struct hw_perf_event *hwc;
 	long err;
 
+	if ((unsigned)cpu >= nr_cpu_ids) {
+		if (!task || cpu != -1)
+			return ERR_PTR(-EINVAL);
+	}
+
 	event = kzalloc(sizeof(*event), GFP_KERNEL);
 	if (!event)
 		return ERR_PTR(-ENOMEM);
@@ -5589,7 +5591,7 @@ perf_event_alloc(struct perf_event_attr 
 
 	if (!overflow_handler && parent_event)
 		overflow_handler = parent_event->overflow_handler;
-	
+
 	event->overflow_handler	= overflow_handler;
 
 	if (attr->disabled)

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