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libbpf: Switch rings to array of pointers

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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: Martin Kelly <martin.kelly@crowdstrike.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230925215045.2375758-3-martin.kelly@crowdstrike.com
This commit is contained in:
Martin Kelly 2023-09-25 14:50:33 -07:00 committed by Andrii Nakryiko
parent 4448f64c54
commit ef3b82003e
1 changed files with 12 additions and 8 deletions
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20
tools/lib/bpf/ringbuf.c
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@ -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)