[PATCH 5/7] perf: Prevent passing zero nr_pages to rb_alloc_aux()

[Adrian Hunter <adrian.hunter@intel.com>]

nr_pages is unsigned long but gets passed to rb_alloc_aux() as an int,
and is stored as an int.

Only power-of-2 values are accepted, so if nr_pages is a 64_bit value, it
will be passed to rb_alloc_aux() as zero.

That is not ideal because:
 1. the value is incorrect
 2. rb_alloc_aux() is at risk of misbehaving, although it manages to
 return -ENOMEM in that case, it is a result of passing zero to get_order()
 even though the get_order() result is documented to be undefined in that
 case.

Fix by simply validating the maximum supported value in the first place.
Use -ENOMEM error code for consistency with the current error code that
is returned in that case.

Fixes: 45bfb2e50471 ("perf: Add AUX area to ring buffer for raw data streams")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 8f908f077935..053e546d5bf0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6509,6 +6509,8 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 			return -EINVAL;
 
 		nr_pages = vma_size / PAGE_SIZE;
+		if (nr_pages > INT_MAX)
+			return -ENOMEM;
 
 		mutex_lock(&event->mmap_mutex);
 		ret = -EINVAL;
-- 
2.34.1