• C
    [AF_UNIX]: Datagram getpeersec · 877ce7c1
    Catherine Zhang 提交于
    This patch implements an API whereby an application can determine the
    label of its peer's Unix datagram sockets via the auxiliary data mechanism of
    recvmsg.
    
    Patch purpose:
    
    This patch enables a security-aware application to retrieve the
    security context of the peer of a Unix datagram socket.  The application
    can then use this security context to determine the security context for
    processing on behalf of the peer who sent the packet.
    
    Patch design and implementation:
    
    The design and implementation is very similar to the UDP case for INET
    sockets.  Basically we build upon the existing Unix domain socket API for
    retrieving user credentials.  Linux offers the API for obtaining user
    credentials via ancillary messages (i.e., out of band/control messages
    that are bundled together with a normal message).  To retrieve the security
    context, the application first indicates to the kernel such desire by
    setting the SO_PASSSEC option via getsockopt.  Then the application
    retrieves the security context using the auxiliary data mechanism.
    
    An example server application for Unix datagram socket should look like this:
    
    toggle = 1;
    toggle_len = sizeof(toggle);
    
    setsockopt(sockfd, SOL_SOCKET, SO_PASSSEC, &toggle, &toggle_len);
    recvmsg(sockfd, &msg_hdr, 0);
    if (msg_hdr.msg_controllen > sizeof(struct cmsghdr)) {
        cmsg_hdr = CMSG_FIRSTHDR(&msg_hdr);
        if (cmsg_hdr->cmsg_len <= CMSG_LEN(sizeof(scontext)) &&
            cmsg_hdr->cmsg_level == SOL_SOCKET &&
            cmsg_hdr->cmsg_type == SCM_SECURITY) {
            memcpy(&scontext, CMSG_DATA(cmsg_hdr), sizeof(scontext));
        }
    }
    
    sock_setsockopt is enhanced with a new socket option SOCK_PASSSEC to allow
    a server socket to receive security context of the peer.
    
    Testing:
    
    We have tested the patch by setting up Unix datagram client and server
    applications.  We verified that the server can retrieve the security context
    using the auxiliary data mechanism of recvmsg.
    Signed-off-by: NCatherine Zhang <cxzhang@watson.ibm.com>
    Acked-by: NAcked-by: James Morris <jmorris@namei.org>
    Signed-off-by: NDavid S. Miller <davem@davemloft.net>
    877ce7c1
socket.h 1.2 KB