net: Fix security_socket_sendmsg() bypass problem.

The sendmmsg() introduced by commit 228e548e "net: Add sendmmsg socket system
call" is capable of sending to multiple different destination addresses.

SMACK is using destination's address for checking sendmsg() permission.
However, security_socket_sendmsg() is called for only once even if multiple
different destination addresses are passed to sendmmsg().

Therefore, we need to call security_socket_sendmsg() for each destination
address rather than only the first destination address.

Since calling security_socket_sendmsg() every time when only single destination
address was passed to sendmmsg() is a waste of time, omit calling
security_socket_sendmsg() unless destination address of previous datagram and
that of current datagram differs.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Anton Blanchard <anton@samba.org>
Cc: stable <stable@kernel.org> [3.0+]
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 9 deletions

diff --git a/net/socket.c b/net/socket.c
index b5c6de4f268a..24a77400b65e 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1871,8 +1871,14 @@ SYSCALL_DEFINE2(shutdown, int, fd, int, how)
 #define COMPAT_NAMELEN(msg)     COMPAT_MSG(msg, msg_namelen)
 #define COMPAT_FLAGS(msg)       COMPAT_MSG(msg, msg_flags)
 
+struct used_address {
+        struct sockaddr_storage name;
+        unsigned int name_len;
+};
+
 static int __sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
-                         struct msghdr *msg_sys, unsigned flags, int nosec)
+                         struct msghdr *msg_sys, unsigned flags,
+                         struct used_address *used_address)
 {
         struct compat_msghdr __user *msg_compat =
             (struct compat_msghdr __user *)msg;
@@ -1953,8 +1959,28 @@ static int __sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
 
         if (sock->file->f_flags & O_NONBLOCK)
                 msg_sys->msg_flags |= MSG_DONTWAIT;
-        err = (nosec ? sock_sendmsg_nosec : sock_sendmsg)(sock, msg_sys,
-                                                          total_len);
+        /*
+         * If this is sendmmsg() and current destination address is same as
+         * previously succeeded address, omit asking LSM's decision.
+         * used_address->name_len is initialized to UINT_MAX so that the first
+         * destination address never matches.
+         */
+        if (used_address && used_address->name_len == msg_sys->msg_namelen &&
+            !memcmp(&used_address->name, msg->msg_name,
+                    used_address->name_len)) {
+                err = sock_sendmsg_nosec(sock, msg_sys, total_len);
+                goto out_freectl;
+        }
+        err = sock_sendmsg(sock, msg_sys, total_len);
+        /*
+         * If this is sendmmsg() and sending to current destination address was
+         * successful, remember it.
+         */
+        if (used_address && err >= 0) {
+                used_address->name_len = msg_sys->msg_namelen;
+                memcpy(&used_address->name, msg->msg_name,
+                       used_address->name_len);
+        }
 
 out_freectl:
         if (ctl_buf != ctl)
@@ -1979,7 +2005,7 @@ SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned, flags)
         if (!sock)
                 goto out;
 
-        err = __sys_sendmsg(sock, msg, &msg_sys, flags, 0);
+        err = __sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
 
         fput_light(sock->file, fput_needed);
 out:
@@ -1998,6 +2024,7 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
         struct mmsghdr __user *entry;
         struct compat_mmsghdr __user *compat_entry;
         struct msghdr msg_sys;
+        struct used_address used_address;
 
         if (vlen > UIO_MAXIOV)
                 vlen = UIO_MAXIOV;
@@ -2008,24 +2035,22 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
         if (!sock)
                 return err;
 
+        used_address.name_len = UINT_MAX;
         entry = mmsg;
         compat_entry = (struct compat_mmsghdr __user *)mmsg;
         err = 0;
 
         while (datagrams < vlen) {
-                /*
-                 * No need to ask LSM for more than the first datagram.
-                 */
                 if (MSG_CMSG_COMPAT & flags) {
                         err = __sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
-                                            &msg_sys, flags, datagrams);
+                                            &msg_sys, flags, &used_address);
                         if (err < 0)
                                 break;
                         err = __put_user(err, &compat_entry->msg_len);
                         ++compat_entry;
                 } else {
                         err = __sys_sendmsg(sock, (struct msghdr __user *)entry,
-                                            &msg_sys, flags, datagrams);
+                                            &msg_sys, flags, &used_address);
                         if (err < 0)
                                 break;
                         err = put_user(err, &entry->msg_len);