Re: [PATCH v2 bpf-next] libbpf: Fix signed overflow in ringbuf_process_ring
From: Andrii Nakryiko <hidden>
Date: 2021-05-05 00:37:46
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On Tue, May 4, 2021 at 2:01 AM Brendan Jackman [off-list ref] wrote:
quoted hunk ↗ jump to hunk
On Mon, 3 May 2021 at 19:46, Andrii Nakryiko [off-list ref] wrote:quoted
On Mon, May 3, 2021 at 5:01 AM Brendan Jackman [off-list ref] wrote:quoted
On Fri, 30 Apr 2021 at 18:31, Andrii Nakryiko [off-list ref] wrote:quoted
So while doing that I noticed that you didn't fix ring_buffer__poll(), so I had to fix it up a bit more extensively. Please check the end result in bpf tree and let me know if there are any problems with it: 2a30f9440640 ("libbpf: Fix signed overflow in ringbuf_process_ring")Ah, thanks for that. Yep, the additional fix looks good to me. I think it actually fixes another very niche issue: 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, inttimeout_ms) return err; res += err; } - return cnt < 0 ? -errno : res; If the callback returns an error but errno is 0 this fails to report the error.
Yeah, there was no need to be clever about that. Explicit if (cnt < 0) check is obvious and correct.
errno(3) says "the value of errno is never set to zero by any system call or library function" but then describes a scenario where an application might usefully set it to zero itself. Maybe it can also be 0 in new threads, depending on your metaphysical interpretation of "by a system call or library function". + if (res > INT_MAX) + return INT_MAX; + return res;