[PATCH 5.4] tracing/ring-buffer: Only do full wait when cpu != RING_BUFFER_ALL_CPUS

[Pratyush Yadav <ptyadav@amazon.de>]

full_hit() directly uses cpu as an array index. Since
RING_BUFFER_ALL_CPUS == -1, calling full_hit() with cpu ==
RING_BUFFER_ALL_CPUS will cause an invalid memory access.

The upstream commit 42fb0a1e84ff ("tracing/ring-buffer: Have polling
block on watermark") already does this. This was missed when backporting
to v5.4.y.

This bug was discovered and resolved using Coverity Static Analysis
Security Testing (SAST) by Synopsys, Inc.

Fixes: e65ac2bdda54 ("tracing/ring-buffer: Have polling block on watermark")
Signed-off-by: Pratyush Yadav <ptyadav@amazon.de>
---

I am not familiar with this code. This was just pointed out by our
static analysis tool and I wrote a quick patch fixing this. Only
compile-tested.

 kernel/trace/ring_buffer.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 176d858903bd..11e8189dd8ae 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -727,6 +727,7 @@ __poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,

 	if (cpu == RING_BUFFER_ALL_CPUS) {
 		work = &buffer->irq_work;
+		full = 0;
 	} else {
 		if (!cpumask_test_cpu(cpu, buffer->cpumask))
 			return -EINVAL;
--
2.38.1




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