[tip: perf/core] perf: Prevent passing zero nr_pages to rb_alloc_aux()

[tip-bot2 for Adrian Hunter]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     dbc48c8f41c208082cfa95e973560134489e3309
Gitweb:        https://git.kernel.org/tip/dbc48c8f41c208082cfa95e973560134489e3309
Author:        Adrian Hunter <adrian.hunter@xxxxxxxxx>
AuthorDate:    Mon, 24 Jun 2024 23:10:59 +03:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 04 Jul 2024 16:00:22 +02:00

perf: Prevent passing zero nr_pages to rb_alloc_aux()

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@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240624201101.60186-6-adrian.hunter@xxxxxxxxx
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6b0a66e..e70d3dd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6496,6 +6496,8 @@ 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;