[PATCH] libbpf:fix use empty function pointers in ringbuf_poll

[Xin Liu]

From: zhangmingyi <zhangmingyi5@xxxxxxxxxx>

The sample_cb of the ring_buffer__new interface can transfer NULL. However,
the system does not check whether sample_cb is NULL during 
ring_buffer__poll, null pointer is used.

Signed-off-by: zhangmingyi <zhangmingyi5@xxxxxxxxxx>
---
 tools/lib/bpf/ringbuf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 02199364db13..3661338a1d2e 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -248,7 +248,7 @@ static int64_t ringbuf_process_ring(struct ring *r)
 			got_new_data = true;
 			cons_pos += roundup_len(len);
 
-			if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) {
+			if (r->sample_cb && ((len & BPF_RINGBUF_DISCARD_BIT) == 0)) {
 				sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ;
 				err = r->sample_cb(r->ctx, sample, len);
 				if (err < 0) {
-- 
2.33.0