mctp: handle the struct sockaddr_mctp padding fields

In order to have the padding fields actually usable in the future,
there have to be checks that user space doesn't supply non-zero garbage
there.  It is also worth setting these padding fields to zero, unless
it is known that they have been already zeroed.

Cc: stable@vger.kernel.org # v5.15
Fixes: 5a20dd46b8b84593 ("mctp: Be explicit about struct sockaddr_mctp padding")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Acked-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mctp/af_mctp.c b/net/mctp/af_mctp.c
index d344b02a1cde68975d15e6eeee9d623958c9b3bd..bc88159f88446d4afa10514104b95349c581eb7d 100644 (file)
--- a/net/mctp/af_mctp.c
+++ b/net/mctp/af_mctp.c
@@ -33,6 +33,12 @@ static int mctp_release(struct socket *sock)
        return 0;
 }
 
+/* Generic sockaddr checks, padding checks only so far */
+static bool mctp_sockaddr_is_ok(const struct sockaddr_mctp *addr)
+{
+       return !addr->__smctp_pad0 && !addr->__smctp_pad1;
+}
+
 static int mctp_bind(struct socket *sock, struct sockaddr *addr, int addrlen)
 {
        struct sock *sk = sock->sk;
@@ -52,6 +58,9 @@ static int mctp_bind(struct socket *sock, struct sockaddr *addr, int addrlen)
        /* it's a valid sockaddr for MCTP, cast and do protocol checks */
        smctp = (struct sockaddr_mctp *)addr;
 
+       if (!mctp_sockaddr_is_ok(smctp))
+               return -EINVAL;
+
        lock_sock(sk);
 
        /* TODO: allow rebind */
@@ -87,6 +96,8 @@ static int mctp_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
                        return -EINVAL;
                if (addr->smctp_family != AF_MCTP)
                        return -EINVAL;
+               if (!mctp_sockaddr_is_ok(addr))
+                       return -EINVAL;
                if (addr->smctp_tag & ~(MCTP_TAG_MASK | MCTP_TAG_OWNER))
                        return -EINVAL;
 
@@ -198,11 +209,13 @@ static int mctp_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 
                addr = msg->msg_name;
                addr->smctp_family = AF_MCTP;
+               addr->__smctp_pad0 = 0;
                addr->smctp_network = cb->net;
                addr->smctp_addr.s_addr = hdr->src;
                addr->smctp_type = type;
                addr->smctp_tag = hdr->flags_seq_tag &
                                        (MCTP_HDR_TAG_MASK | MCTP_HDR_FLAG_TO);
+               addr->__smctp_pad1 = 0;
                msg->msg_namelen = sizeof(*addr);
 
                if (msk->addr_ext) {