libbpf: fix invalid munmap call

When unmapping the AF_XDP memory regions used for the rings, an
invalid address was passed to the munmap() calls. Instead of passing
the beginning of the memory region, the descriptor region was passed
to munmap.

When the userspace application tried to tear down an AF_XDP socket,
the operation failed and the application would still have a reference
to socket it wished to get rid of.
Reported-by: NWilliam Tu <u9012063@gmail.com>
Fixes: 1cad0788 ("libbpf: add support for using AF_XDP sockets")
Signed-off-by: NBjörn Töpel <bjorn.topel@intel.com>
Tested-by: NWilliam Tu <u9012063@gmail.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>

tools/lib/bpf/xsk.c

@@ -248,8 +248,7 @@ int xsk_umem__create(struct xsk_umem **umem_ptr, void *umem_area, __u64 size,
 	return 0;
 
 out_mmap:
-	munmap(umem->fill,
-	       off.fr.desc + umem->config.fill_size * sizeof(__u64));
+	munmap(map, off.fr.desc + umem->config.fill_size * sizeof(__u64));
 out_socket:
 	close(umem->fd);
 out_umem_alloc:
@@ -524,11 +523,11 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
 		       struct xsk_ring_cons *rx, struct xsk_ring_prod *tx,
 		       const struct xsk_socket_config *usr_config)
 {
+	void *rx_map = NULL, *tx_map = NULL;
 	struct sockaddr_xdp sxdp = {};
 	struct xdp_mmap_offsets off;
 	struct xsk_socket *xsk;
 	socklen_t optlen;
-	void *map;
 	int err;
 
 	if (!umem || !xsk_ptr || !rx || !tx)
@@ -594,40 +593,40 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
 	}
 
 	if (rx) {
-		map = xsk_mmap(NULL, off.rx.desc +
-			       xsk->config.rx_size * sizeof(struct xdp_desc),
-			       PROT_READ | PROT_WRITE,
-			       MAP_SHARED | MAP_POPULATE,
-			       xsk->fd, XDP_PGOFF_RX_RING);
-		if (map == MAP_FAILED) {
+		rx_map = xsk_mmap(NULL, off.rx.desc +
+				  xsk->config.rx_size * sizeof(struct xdp_desc),
+				  PROT_READ | PROT_WRITE,
+				  MAP_SHARED | MAP_POPULATE,
+				  xsk->fd, XDP_PGOFF_RX_RING);
+		if (rx_map == MAP_FAILED) {
 			err = -errno;
 			goto out_socket;
 		}
 
 		rx->mask = xsk->config.rx_size - 1;
 		rx->size = xsk->config.rx_size;
-		rx->producer = map + off.rx.producer;
-		rx->consumer = map + off.rx.consumer;
-		rx->ring = map + off.rx.desc;
+		rx->producer = rx_map + off.rx.producer;
+		rx->consumer = rx_map + off.rx.consumer;
+		rx->ring = rx_map + off.rx.desc;
 	}
 	xsk->rx = rx;
 
 	if (tx) {
-		map = xsk_mmap(NULL, off.tx.desc +
-			       xsk->config.tx_size * sizeof(struct xdp_desc),
-			       PROT_READ | PROT_WRITE,
-			       MAP_SHARED | MAP_POPULATE,
-			       xsk->fd, XDP_PGOFF_TX_RING);
-		if (map == MAP_FAILED) {
+		tx_map = xsk_mmap(NULL, off.tx.desc +
+				  xsk->config.tx_size * sizeof(struct xdp_desc),
+				  PROT_READ | PROT_WRITE,
+				  MAP_SHARED | MAP_POPULATE,
+				  xsk->fd, XDP_PGOFF_TX_RING);
+		if (tx_map == MAP_FAILED) {
 			err = -errno;
 			goto out_mmap_rx;
 		}
 
 		tx->mask = xsk->config.tx_size - 1;
 		tx->size = xsk->config.tx_size;
-		tx->producer = map + off.tx.producer;
-		tx->consumer = map + off.tx.consumer;
-		tx->ring = map + off.tx.desc;
+		tx->producer = tx_map + off.tx.producer;
+		tx->consumer = tx_map + off.tx.consumer;
+		tx->ring = tx_map + off.tx.desc;
 		tx->cached_cons = xsk->config.tx_size;
 	}
 	xsk->tx = tx;
@@ -654,13 +653,11 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
 
 out_mmap_tx:
 	if (tx)
-		munmap(xsk->tx,
-		       off.tx.desc +
+		munmap(tx_map, off.tx.desc +
 		       xsk->config.tx_size * sizeof(struct xdp_desc));
 out_mmap_rx:
 	if (rx)
-		munmap(xsk->rx,
-		       off.rx.desc +
+		munmap(rx_map, off.rx.desc +
 		       xsk->config.rx_size * sizeof(struct xdp_desc));
 out_socket:
 	if (--umem->refcount)
@@ -685,10 +682,12 @@ int xsk_umem__delete(struct xsk_umem *umem)
 	optlen = sizeof(off);
 	err = getsockopt(umem->fd, SOL_XDP, XDP_MMAP_OFFSETS, &off, &optlen);
 	if (!err) {
-		munmap(umem->fill->ring,
-		       off.fr.desc + umem->config.fill_size * sizeof(__u64));
-		munmap(umem->comp->ring,
-		       off.cr.desc + umem->config.comp_size * sizeof(__u64));
+		(void)munmap(umem->fill->ring - off.fr.desc,
+			     off.fr.desc +
+			     umem->config.fill_size * sizeof(__u64));
+		(void)munmap(umem->comp->ring - off.cr.desc,
+			     off.cr.desc +
+			     umem->config.comp_size * sizeof(__u64));
 	}
 
 	close(umem->fd);
@@ -699,6 +698,7 @@ int xsk_umem__delete(struct xsk_umem *umem)
 
 void xsk_socket__delete(struct xsk_socket *xsk)
 {
+	size_t desc_sz = sizeof(struct xdp_desc);
 	struct xdp_mmap_offsets off;
 	socklen_t optlen;
 	int err;
@@ -711,14 +711,17 @@ void xsk_socket__delete(struct xsk_socket *xsk)
 	optlen = sizeof(off);
 	err = getsockopt(xsk->fd, SOL_XDP, XDP_MMAP_OFFSETS, &off, &optlen);
 	if (!err) {
-		if (xsk->rx)
-			munmap(xsk->rx->ring,
-			       off.rx.desc +
-			       xsk->config.rx_size * sizeof(struct xdp_desc));
-		if (xsk->tx)
-			munmap(xsk->tx->ring,
-			       off.tx.desc +
-			       xsk->config.tx_size * sizeof(struct xdp_desc));
+		if (xsk->rx) {
+			(void)munmap(xsk->rx->ring - off.rx.desc,
+				     off.rx.desc +
+				     xsk->config.rx_size * desc_sz);
+		}
+		if (xsk->tx) {
+			(void)munmap(xsk->tx->ring - off.tx.desc,
+				     off.tx.desc +
+				     xsk->config.tx_size * desc_sz);
+		}
+
 	}
 
 	xsk->umem->refcount--;