sunrpc: fix handling of server side tls alerts

Scott Mayhew discovered a security exploit in NFS over TLS in
tls_alert_recv() due to its assumption it can read data from
the msg iterator's kvec..

kTLS implementation splits TLS non-data record payload between
the control message buffer (which includes the type such as TLS
aler or TLS cipher change) and the rest of the payload (say TLS
alert's level/description) which goes into the msg payload buffer.

This patch proposes to rework how control messages are setup and
used by sock_recvmsg().

If no control message structure is setup, kTLS layer will read and
process TLS data record types. As soon as it encounters a TLS control
message, it would return an error. At that point, NFS can setup a
kvec backed msg buffer and read in the control message such as a
TLS alert. Msg iterator can advance the kvec pointer as a part of
the copy process thus we need to revert the iterator before calling
into the tls_alert_recv.

Reported-by: Scott Mayhew <smayhew@redhat.com>
Fixes: 5e052dda121e ("SUNRPC: Recognize control messages in server-side TCP socket code")
Suggested-by: Trond Myklebust <trondmy@hammerspace.com>
Cc: stable@vger.kernel.org
Signed-off-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 46c156b121db43c1bd1806a08a3a9bf08b332699..e2c5e0e626f9484490bd12c59941a69bda93ac3e 100644 (file)
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -257,20 +257,47 @@ svc_tcp_sock_process_cmsg(struct socket *sock, struct msghdr *msg,
 }
 
 static int
-svc_tcp_sock_recv_cmsg(struct svc_sock *svsk, struct msghdr *msg)
+svc_tcp_sock_recv_cmsg(struct socket *sock, unsigned int *msg_flags)
 {
        union {
                struct cmsghdr  cmsg;
                u8              buf[CMSG_SPACE(sizeof(u8))];
        } u;
-       struct socket *sock = svsk->sk_sock;
+       u8 alert[2];
+       struct kvec alert_kvec = {
+               .iov_base = alert,
+               .iov_len = sizeof(alert),
+       };
+       struct msghdr msg = {
+               .msg_flags = *msg_flags,
+               .msg_control = &u,
+               .msg_controllen = sizeof(u),
+       };
+       int ret;
+
+       iov_iter_kvec(&msg.msg_iter, ITER_DEST, &alert_kvec, 1,
+                     alert_kvec.iov_len);
+       ret = sock_recvmsg(sock, &msg, MSG_DONTWAIT);
+       if (ret > 0 &&
+           tls_get_record_type(sock->sk, &u.cmsg) == TLS_RECORD_TYPE_ALERT) {
+               iov_iter_revert(&msg.msg_iter, ret);
+               ret = svc_tcp_sock_process_cmsg(sock, &msg, &u.cmsg, -EAGAIN);
+       }
+       return ret;
+}
+
+static int
+svc_tcp_sock_recvmsg(struct svc_sock *svsk, struct msghdr *msg)
+{
        int ret;
+       struct socket *sock = svsk->sk_sock;
 
-       msg->msg_control = &u;
-       msg->msg_controllen = sizeof(u);
        ret = sock_recvmsg(sock, msg, MSG_DONTWAIT);
-       if (unlikely(msg->msg_controllen != sizeof(u)))
-               ret = svc_tcp_sock_process_cmsg(sock, msg, &u.cmsg, ret);
+       if (msg->msg_flags & MSG_CTRUNC) {
+               msg->msg_flags &= ~(MSG_CTRUNC | MSG_EOR);
+               if (ret == 0 || ret == -EIO)
+                       ret = svc_tcp_sock_recv_cmsg(sock, &msg->msg_flags);
+       }
        return ret;
 }
 
@@ -321,7 +348,7 @@ static ssize_t svc_tcp_read_msg(struct svc_rqst *rqstp, size_t buflen,
                iov_iter_advance(&msg.msg_iter, seek);
                buflen -= seek;
        }
-       len = svc_tcp_sock_recv_cmsg(svsk, &msg);
+       len = svc_tcp_sock_recvmsg(svsk, &msg);
        if (len > 0)
                svc_flush_bvec(bvec, len, seek);
 
@@ -1018,7 +1045,7 @@ static ssize_t svc_tcp_read_marker(struct svc_sock *svsk,
                iov.iov_base = ((char *)&svsk->sk_marker) + svsk->sk_tcplen;
                iov.iov_len  = want;
                iov_iter_kvec(&msg.msg_iter, ITER_DEST, &iov, 1, want);
-               len = svc_tcp_sock_recv_cmsg(svsk, &msg);
+               len = svc_tcp_sock_recvmsg(svsk, &msg);
                if (len < 0)
                        return len;
                svsk->sk_tcplen += len;