libbpf: Refactor cleanup in ring_buffer__add

Refactor the cleanup code in ring_buffer__add to use a unified err_out
label. This reduces code duplication, as well as plugging a potential
leak if mmap_sz != (__u64)(size_t)mmap_sz (currently this would miss
unmapping tmp because ringbuf_unmap_ring isn't called).

Signed-off-by: Martin Kelly <martin.kelly@crowdstrike.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230925215045.2375758-2-martin.kelly@crowdstrike.com

diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index 0219936..29b0d19 100644 (file)
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -121,7 +121,7 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
                err = -errno;
                pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
                        map_fd, err);
-               return libbpf_err(err);
+               goto err_out;
        }
        r->consumer_pos = tmp;
 
@@ -131,16 +131,16 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
         */
        mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
        if (mmap_sz != (__u64)(size_t)mmap_sz) {
+               err = -E2BIG;
                pr_warn("ringbuf: ring buffer size (%u) is too big\n", info.max_entries);
-               return libbpf_err(-E2BIG);
+               goto err_out;
        }
        tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ, MAP_SHARED, map_fd, rb->page_size);
        if (tmp == MAP_FAILED) {
                err = -errno;
-               ringbuf_unmap_ring(rb, r);
                pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
                        map_fd, err);
-               return libbpf_err(err);
+               goto err_out;
        }
        r->producer_pos = tmp;
        r->data = tmp + rb->page_size;
@@ -152,14 +152,17 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
        e->data.fd = rb->ring_cnt;
        if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
                err = -errno;
-               ringbuf_unmap_ring(rb, r);
                pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
                        map_fd, err);
-               return libbpf_err(err);
+               goto err_out;
        }
 
        rb->ring_cnt++;
        return 0;
+
+err_out:
+       ringbuf_unmap_ring(rb, r);
+       return libbpf_err(err);
 }
 
 void ring_buffer__free(struct ring_buffer *rb)