vsock: check socket family before reading sockaddr

Extracting a helper function for this has the nice side effect of
making the `cid' and `port' parameters to vsock_accept nullable, which
is nice for consistency with vsock_get_cid_and_port.

Message-Id: <20210319025648.17925-2-hi@alyssa.is>
Reviewed-by: Cole Helbling <cole.e.helbling@outlook.com>

2 files changed, 33 insertions, 9 deletions

diff --git a/vsock.c b/vsock.c
index 99945c3..6f1f466 100644
--- a/vsock.c
+++ b/vsock.c
@@ -5,6 +5,7 @@
 
 #include "vsock.h"
 
+#include <errno.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 
@@ -17,6 +18,25 @@ static void fill_sockaddr(struct sockaddr_vm *addr, uint32_t cid, uint32_t port)
 	addr->svm_port = port;
 }
 
+static int fill_cid_and_port(const struct sockaddr_vm *addr,
+			     uint32_t *cid, uint32_t *port)
+{
+	// Check that this sockaddr info is actually for the socket
+	// type we think it is, or we could get some very confusing
+	// data out of it.
+	if (addr->svm_family != AF_VSOCK) {
+		errno = EPROTOTYPE;
+		return -1;
+	}
+
+	if (cid)
+		*cid = addr->svm_cid;
+	if (port)
+		*port = addr->svm_port;
+
+	return 0;
+}
+
 int vsock_bind(int fd, uint32_t cid, uint32_t port)
 {
 	struct sockaddr_vm addr = { 0 };
@@ -37,8 +57,8 @@ int vsock_accept(int sockfd, uint32_t *cid, uint32_t *port)
 	if ((fd = accept(sockfd, (struct sockaddr *)&addr, &addr_size)) == -1)
 		return -1;
 
-	*cid = addr.svm_cid;
-	*port = addr.svm_port;
+	if (fill_cid_and_port(&addr, cid, port) == -1)
+		return -1;
 
 	return fd;
 }
@@ -70,10 +90,5 @@ int vsock_get_cid_and_port(int fd, uint32_t *cid, uint32_t *port)
 	if (getsockname(fd, (struct sockaddr *)&addr, &addrlen) == -1)
 		return -1;
 
-	if (cid)
-		*cid = addr.svm_cid;
-	if (port)
-		*port = addr.svm_port;
-
-	return 0;
+	return fill_cid_and_port(&addr, cid, port);
 }
diff --git a/vsock.h b/vsock.h
index e7ffd62..0b7d157 100644
--- a/vsock.h
+++ b/vsock.h
@@ -3,11 +3,20 @@
 
 #include <stdint.h>
 
+// All functions taking `cid'/`port' output parameters will fail with
+// EPROTOTYPE if the given file descriptor is not an AF_VSOCK socket.
+// The socket is left in an undefined state after this.
+//
+// `cid'/`port' output parameters can be NULL if the information is
+// not required.
+//
+// A return value of -1 indicates failure.  `errno' can be consulted for
+// further information.
+
 int vsock_bind(int fd, uint32_t cid, uint32_t port);
 int vsock_accept(int sockfd, uint32_t *cid, uint32_t *port);
 
 int vsock_connect(int fd, uint32_t cid, uint32_t port);
 int vsock_open(uint32_t cid, uint32_t port);
 
-// `cid' and `port' can be null.
 int vsock_get_cid_and_port(int fd, uint32_t *cid, uint32_t *port);