Commit ef3b8200 authored by Martin Kelly's avatar Martin Kelly Committed by Andrii Nakryiko
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libbpf: Switch rings to array of pointers 



Switch rb->rings to be an array of pointers instead of a contiguous
block. This allows for each ring pointer to be stable after
ring_buffer__add is called, which allows us to expose struct ring * to
the user without gotchas. Without this change, the realloc in
ring_buffer__add could invalidate a struct ring *, making it unsafe to
give to the user.

Signed-off-by: default avatarMartin Kelly <martin.kelly@crowdstrike.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230925215045.2375758-3-martin.kelly@crowdstrike.com
parent 4448f64c

tools/lib/bpf/ringbuf.c

+12 −8
Original line number Diff line number Diff line
@@ -34,7 +34,7 @@ struct ring { 


struct ring_buffer {

	struct epoll_event *events;

	struct ring *rings;

	struct ring **rings;

	size_t page_size;

	int epoll_fd;

	int ring_cnt;
@@ -57,7 +57,7 @@ struct ringbuf_hdr { 
	__u32 pad;

};



static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r)

static void ringbuf_free_ring(struct ring_buffer *rb, struct ring *r)

{

	if (r->consumer_pos) {

		munmap(r->consumer_pos, rb->page_size);
@@ -67,6 +67,8 @@ static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r) 
		munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));

		r->producer_pos = NULL;

	}



	free(r);

}



/* Add extra RINGBUF maps to this ring buffer manager */
@@ -107,8 +109,10 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd, 
		return libbpf_err(-ENOMEM);

	rb->events = tmp;



	r = &rb->rings[rb->ring_cnt];

	memset(r, 0, sizeof(*r));

	r = calloc(1, sizeof(*r));

	if (!r)

		return libbpf_err(-ENOMEM);

	rb->rings[rb->ring_cnt] = r;



	r->map_fd = map_fd;

	r->sample_cb = sample_cb;
@@ -161,7 +165,7 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd, 
	return 0;



err_out:

	ringbuf_unmap_ring(rb, r);

	ringbuf_free_ring(rb, r);

	return libbpf_err(err);

}
@@ -173,7 +177,7 @@ void ring_buffer__free(struct ring_buffer *rb) 
		return;



	for (i = 0; i < rb->ring_cnt; ++i)

		ringbuf_unmap_ring(rb, &rb->rings[i]);

		ringbuf_free_ring(rb, rb->rings[i]);

	if (rb->epoll_fd >= 0)

		close(rb->epoll_fd);
@@ -281,7 +285,7 @@ int ring_buffer__consume(struct ring_buffer *rb) 
	int i;



	for (i = 0; i < rb->ring_cnt; i++) {

		struct ring *ring = &rb->rings[i];

		struct ring *ring = rb->rings[i];



		err = ringbuf_process_ring(ring);

		if (err < 0)
@@ -308,7 +312,7 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms) 


	for (i = 0; i < cnt; i++) {

		__u32 ring_id = rb->events[i].data.fd;

		struct ring *ring = &rb->rings[ring_id];

		struct ring *ring = rb->rings[ring_id];



		err = ringbuf_process_ring(ring);

		if (err < 0)