[PATCH bpf v2 2/4] libbpf: Handle size overflow for ringbuf mmap

[Hou Tao <houtao@huaweicloud.com>]

From: Hou Tao <houtao1@huawei.com>

The maximum size of ringbuf is 2GB on x86-64 host, so 2 * max_entries
will overflow u32 when mapping producer page and data pages. Only
casting max_entries to size_t is not enough, because for 32-bits
application on 64-bits kernel the size of read-only mmap region
also could overflow size_t.

So fixing it by casting the size of read-only mmap region into a __u64
and checking whether or not there will be overflow during mmap.

Fixes: bf99c936f947 ("libbpf: Add BPF ring buffer support")
Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 tools/lib/bpf/ringbuf.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index d285171d4b69..5b1dc8794b06 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -77,6 +77,7 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 	__u32 len = sizeof(info);
 	struct epoll_event *e;
 	struct ring *r;
+	__u64 mmap_sz;
 	void *tmp;
 	int err;
 
@@ -129,8 +130,14 @@ int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 	 * data size to allow simple reading of samples that wrap around the
 	 * end of a ring buffer. See kernel implementation for details.
 	 * */
-	tmp = mmap(NULL, rb->page_size + 2 * info.max_entries, PROT_READ,
-		   MAP_SHARED, map_fd, rb->page_size);
+	mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
+	if (mmap_sz != (__u64)(size_t)mmap_sz) {
+		pr_warn("ringbuf: ring buffer size (%u) is too big\n",
+			info.max_entries);
+		return libbpf_err(-E2BIG);
+	}
+	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);
-- 
2.29.2