Commit 2a30f944 authored by Brendan Jackman's avatar Brendan Jackman Committed by Andrii Nakryiko
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libbpf: Fix signed overflow in ringbuf_process_ring 



One of our benchmarks running in (Google-internal) CI pushes data
through the ringbuf faster htan than userspace is able to consume
it. In this case it seems we're actually able to get >INT_MAX entries
in a single ring_buffer__consume() call. ASAN detected that cnt
overflows in this case.

Fix by using 64-bit counter internally and then capping the result to
INT_MAX before converting to the int return type. Do the same for
the ring_buffer__poll().

Fixes: bf99c936 (libbpf: Add BPF ring buffer support)
Signed-off-by: default avatarBrendan Jackman <jackmanb@google.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210429130510.1621665-1-jackmanb@google.com
parent 801c6058

tools/lib/bpf/ringbuf.c

+21 −9
Original line number Diff line number Diff line
@@ -202,9 +202,11 @@ static inline int roundup_len(__u32 len) 
	return (len + 7) / 8 * 8;

}



static int ringbuf_process_ring(struct ring* r)

static int64_t ringbuf_process_ring(struct ring* r)

{

	int *len_ptr, len, err, cnt = 0;

	int *len_ptr, len, err;

	/* 64-bit to avoid overflow in case of extreme application behavior */

	int64_t cnt = 0;

	unsigned long cons_pos, prod_pos;

	bool got_new_data;

	void *sample;
@@ -244,12 +246,14 @@ static int ringbuf_process_ring(struct ring* r) 
}



/* Consume available ring buffer(s) data without event polling.

 * Returns number of records consumed across all registered ring buffers, or

 * negative number if any of the callbacks return error.

 * Returns number of records consumed across all registered ring buffers (or

 * INT_MAX, whichever is less), or negative number if any of the callbacks

 * return error.

 */

int ring_buffer__consume(struct ring_buffer *rb)

{

	int i, err, res = 0;

	int64_t err, res = 0;

	int i;



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

		struct ring *ring = &rb->rings[i];
@@ -259,18 +263,24 @@ int ring_buffer__consume(struct ring_buffer *rb) 
			return err;

		res += err;

	}

	if (res > INT_MAX)

		return INT_MAX;

	return res;

}



/* Poll for available data and consume records, if any are available.

 * Returns number of records consumed, or negative number, if any of the

 * registered callbacks returned error.

 * Returns number of records consumed (or INT_MAX, whichever is less), or

 * negative number, if any of the registered callbacks returned error.

 */

int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)

{

	int i, cnt, err, res = 0;

	int i, cnt;

	int64_t err, res = 0;



	cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);

	if (cnt < 0)

		return -errno;



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

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

		struct ring *ring = &rb->rings[ring_id];
@@ -280,7 +290,9 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms) 
			return err;

		res += err;

	}

	return cnt < 0 ? -errno : res;

	if (res > INT_MAX)

		return INT_MAX;

	return res;

}



/* Get an fd that can be used to sleep until data is available in the ring(s) */