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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: bf99c936f9 (libbpf: Add BPF ring buffer support)
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210429130510.1621665-1-jackmanb@google.com
This commit is contained in:
Brendan Jackman 2021-04-29 13:05:10 +00:00 committed by Andrii Nakryiko
parent 801c6058d1
commit 2a30f94406
1 changed files with 21 additions and 9 deletions
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30
tools/lib/bpf/ringbuf.c
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@ -202,9 +202,11 @@ static inline int roundup_len(__u32 len)
return (len + 7) / 8 * 8; 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; unsigned long cons_pos, prod_pos;
bool got_new_data; bool got_new_data;
void *sample; void *sample;
@ -244,12 +246,14 @@ done:
} }
/* Consume available ring buffer(s) data without event polling. /* Consume available ring buffer(s) data without event polling.
* Returns number of records consumed across all registered ring buffers, or * Returns number of records consumed across all registered ring buffers (or
* negative number if any of the callbacks return error. * INT_MAX, whichever is less), or negative number if any of the callbacks
* return error.
*/ */
int ring_buffer__consume(struct ring_buffer *rb) 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++) { for (i = 0; i < rb->ring_cnt; i++) {
struct ring *ring = &rb->rings[i]; struct ring *ring = &rb->rings[i];
@ -259,18 +263,24 @@ int ring_buffer__consume(struct ring_buffer *rb)
return err; return err;
res += err; res += err;
} }
if (res > INT_MAX)
return INT_MAX;
return res; return res;
} }
/* Poll for available data and consume records, if any are available. /* Poll for available data and consume records, if any are available.
* Returns number of records consumed, or negative number, if any of the * Returns number of records consumed (or INT_MAX, whichever is less), or
* registered callbacks returned error. * negative number, if any of the registered callbacks returned error.
*/ */
int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms) 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); cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
if (cnt < 0)
return -errno;
for (i = 0; i < cnt; i++) { for (i = 0; i < cnt; i++) {
__u32 ring_id = rb->events[i].data.fd; __u32 ring_id = rb->events[i].data.fd;
struct ring *ring = &rb->rings[ring_id]; struct ring *ring = &rb->rings[ring_id];
@ -280,7 +290,9 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
return err; return err;
res += 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) */ /* Get an fd that can be used to sleep until data is available in the ring(s) */