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Commit 15621e09 authored by Geremy Condra's avatar Geremy Condra
Browse files

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
parent 15892e10

include/cutils/uevent.h

+1 −0
Original line number Diff line number Diff line
@@ -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

}

libcutils/uevent.c

+25 −6
Original line number Diff line number Diff line
@@ -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: