From 2c7946a7bf45ae86736ab3b43d0085e43947945c Mon Sep 17 00:00:00 2001 From: Catherine Zhang Date: Mon, 20 Mar 2006 22:41:23 -0800 Subject: [SECURITY]: TCP/UDP getpeersec This patch implements an application of the LSM-IPSec networking controls whereby an application can determine the label of the security association its TCP or UDP sockets are currently connected to via getsockopt and the auxiliary data mechanism of recvmsg. Patch purpose: This patch enables a security-aware application to retrieve the security context of an IPSec security association a particular TCP or UDP socket is using. The application can then use this security context to determine the security context for processing on behalf of the peer at the other end of this connection. In the case of UDP, the security context is for each individual packet. An example application is the inetd daemon, which could be modified to start daemons running at security contexts dependent on the remote client. Patch design approach: - Design for TCP The patch enables the SELinux LSM to set the peer security context for a socket based on the security context of the IPSec security association. The application may retrieve this context using getsockopt. When called, the kernel determines if the socket is a connected (TCP_ESTABLISHED) TCP socket and, if so, uses the dst_entry cache on the socket to retrieve the security associations. If a security association has a security context, the context string is returned, as for UNIX domain sockets. - Design for UDP Unlike TCP, UDP is connectionless. This requires a somewhat different API to retrieve the peer security context. With TCP, the peer security context stays the same throughout the connection, thus it can be retrieved at any time between when the connection is established and when it is torn down. With UDP, each read/write can have different peer and thus the security context might change every time. As a result the security context retrieval must be done TOGETHER with the packet retrieval. The solution is to 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). Patch implementation details: - Implementation for TCP The security context can be retrieved by applications using getsockopt with the existing SO_PEERSEC flag. As an example (ignoring error checking): getsockopt(sockfd, SOL_SOCKET, SO_PEERSEC, optbuf, &optlen); printf("Socket peer context is: %s\n", optbuf); The SELinux function, selinux_socket_getpeersec, is extended to check for labeled security associations for connected (TCP_ESTABLISHED == sk->sk_state) TCP sockets only. If so, the socket has a dst_cache of struct dst_entry values that may refer to security associations. If these have security associations with security contexts, the security context is returned. getsockopt returns a buffer that contains a security context string or the buffer is unmodified. - Implementation for UDP To retrieve the security context, the application first indicates to the kernel such desire by setting the IP_PASSSEC option via getsockopt. Then the application retrieves the security context using the auxiliary data mechanism. An example server application for UDP should look like this: toggle = 1; toggle_len = sizeof(toggle); setsockopt(sockfd, SOL_IP, IP_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_IP && cmsg_hdr->cmsg_type == SCM_SECURITY) { memcpy(&scontext, CMSG_DATA(cmsg_hdr), sizeof(scontext)); } } ip_setsockopt is enhanced with a new socket option IP_PASSSEC to allow a server socket to receive security context of the peer. A new ancillary message type SCM_SECURITY. When the packet is received we get the security context from the sec_path pointer which is contained in the sk_buff, and copy it to the ancillary message space. An additional LSM hook, selinux_socket_getpeersec_udp, is defined to retrieve the security context from the SELinux space. The existing function, selinux_socket_getpeersec does not suit our purpose, because the security context is copied directly to user space, rather than to kernel space. Testing: We have tested the patch by setting up TCP and UDP connections between applications on two machines using the IPSec policies that result in labeled security associations being built. For TCP, we can then extract the peer security context using getsockopt on either end. For UDP, the receiving end can retrieve the security context using the auxiliary data mechanism of recvmsg. Signed-off-by: Catherine Zhang Acked-by: James Morris Acked-by: Herbert Xu Signed-off-by: David S. Miller --- net/core/sock.c | 2 +- net/ipv4/ip_sockglue.c | 31 ++++++++++++++++++++++++++++++- 2 files changed, 31 insertions(+), 2 deletions(-) (limited to 'net') diff --git a/net/core/sock.c b/net/core/sock.c index 6e00811d44bc..5038a5a7bd84 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -616,7 +616,7 @@ int sock_getsockopt(struct socket *sock, int level, int optname, break; case SO_PEERSEC: - return security_socket_getpeersec(sock, optval, optlen, len); + return security_socket_getpeersec_stream(sock, optval, optlen, len); default: return(-ENOPROTOOPT); diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c index 2bf8d782f678..b5c4f61518e8 100644 --- a/net/ipv4/ip_sockglue.c +++ b/net/ipv4/ip_sockglue.c @@ -50,6 +50,7 @@ #define IP_CMSG_TOS 4 #define IP_CMSG_RECVOPTS 8 #define IP_CMSG_RETOPTS 16 +#define IP_CMSG_PASSSEC 32 /* * SOL_IP control messages. @@ -109,6 +110,19 @@ static void ip_cmsg_recv_retopts(struct msghdr *msg, struct sk_buff *skb) put_cmsg(msg, SOL_IP, IP_RETOPTS, opt->optlen, opt->__data); } +static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb) +{ + char *secdata; + u32 seclen; + int err; + + err = security_socket_getpeersec_dgram(skb, &secdata, &seclen); + if (err) + return; + + put_cmsg(msg, SOL_IP, SCM_SECURITY, seclen, secdata); +} + void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb) { @@ -138,6 +152,11 @@ void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb) if (flags & 1) ip_cmsg_recv_retopts(msg, skb); + if ((flags>>=1) == 0) + return; + + if (flags & 1) + ip_cmsg_recv_security(msg, skb); } int ip_cmsg_send(struct msghdr *msg, struct ipcm_cookie *ipc) @@ -393,7 +412,8 @@ int ip_setsockopt(struct sock *sk, int level, int optname, char __user *optval, (1<= sizeof(int)) { @@ -478,6 +498,12 @@ int ip_setsockopt(struct sock *sk, int level, int optname, char __user *optval, else inet->cmsg_flags &= ~IP_CMSG_RETOPTS; break; + case IP_PASSSEC: + if (val) + inet->cmsg_flags |= IP_CMSG_PASSSEC; + else + inet->cmsg_flags &= ~IP_CMSG_PASSSEC; + break; case IP_TOS: /* This sets both TOS and Precedence */ if (sk->sk_type == SOCK_STREAM) { val &= ~3; @@ -932,6 +958,9 @@ int ip_getsockopt(struct sock *sk, int level, int optname, char __user *optval, case IP_RETOPTS: val = (inet->cmsg_flags & IP_CMSG_RETOPTS) != 0; break; + case IP_PASSSEC: + val = (inet->cmsg_flags & IP_CMSG_PASSSEC) != 0; + break; case IP_TOS: val = inet->tos; break; -- cgit v1.2.3