cutils: return the remote uid on netlink recv failure
This change adds a layer of indirection to uevent's
uevent_kernel_multicast_recv, allowing dependent code to
get the remote endpoint if desired.
Change-Id: If2f00708a1dd6196c415b1ebc2a7eeb72399a90e
diff --git a/libcutils/uevent.c b/libcutils/uevent.c
index 4add29c..97a81e3 100644
--- a/libcutils/uevent.c
+++ b/libcutils/uevent.c
@@ -29,7 +29,24 @@
/**
* Like recv(), but checks that messages actually originate from the kernel.
*/
-ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length) {
+ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length)
+{
+ uid_t user = -1;
+ return uevent_kernel_multicast_uid_recv(socket, buffer, length, &user);
+}
+
+/**
+ * Like the above, but passes a uid_t in by reference. In the event that this
+ * fails due to a bad uid check, the uid_t will be set to the uid of the
+ * socket's peer.
+ *
+ * If this method rejects a netlink message from outside the kernel, it
+ * returns -1, sets errno to EIO, and sets "user" to the UID associated with the
+ * message. If the peer UID cannot be determined, "user" is set to -1."
+ */
+ssize_t uevent_kernel_multicast_uid_recv(int socket, void *buffer,
+ size_t length, uid_t *user)
+{
struct iovec iov = { buffer, length };
struct sockaddr_nl addr;
char control[CMSG_SPACE(sizeof(struct ucred))];
@@ -43,16 +60,12 @@
0,
};
+ *user = -1;
ssize_t n = recvmsg(socket, &hdr, 0);
if (n <= 0) {
return n;
}
- if (addr.nl_groups == 0 || addr.nl_pid != 0) {
- /* ignoring non-kernel or unicast netlink message */
- goto out;
- }
-
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);
if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
/* ignoring netlink message with no sender credentials */
@@ -60,11 +73,17 @@
}
struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg);
+ *user = cred->uid;
if (cred->uid != 0) {
/* ignoring netlink message from non-root user */
goto out;
}
+ if (addr.nl_groups == 0 || addr.nl_pid != 0) {
+ /* ignoring non-kernel or unicast netlink message */
+ goto out;
+ }
+
return n;
out: