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cutils: return the remote uid on netlink recv failure

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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
This commit is contained in:
Geremy Condra 2012-03-29 14:46:07 -07:00
parent 15892e10a4
commit 15621e0970
2 changed files with 26 additions and 6 deletions
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1
include/cutils/uevent.h
View file

@ -26,6 +26,7 @@ extern "C" {
int uevent_open_socket(int buf_sz, bool passcred);
ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length);
ssize_t uevent_kernel_multicast_uid_recv(int socket, void *buffer, size_t length, uid_t *uid);
#ifdef __cplusplus
}

31
libcutils/uevent.c
View file

@ -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 @@ ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length) {
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 @@ ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length) {
}
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: