[PATCH net 1/2] mptcp: forbit mcast-related sockopt on MPTCP sockets

[Paolo Abeni]

Unrolling mcast state at msk dismantel time is bug prone, as
syzkaller reported:

======================================================
WARNING: possible circular locking dependency detected
5.11.0-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor905/8822 is trying to acquire lock:
ffffffff8d678fe8 (rtnl_mutex){+.+.}-{3:3}, at: ipv6_sock_mc_close+0xd7/0x110 
net/ipv6/mcast.c:323

but task is already holding lock:
ffff888024390120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock 
include/net/sock.h:1600 [inline]
ffff888024390120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp6_release+0x57/0x130 
net/mptcp/protocol.c:3507

which lock already depends on the new lock.

Instead we can simply forbit any mcast-related setsockopt

Fixes: 717e79c867ca5 ("mptcp: Add setsockopt()/getsockopt() socket operations")
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 net/mptcp/protocol.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 1590b9d4cde2..e06cea0a3c54 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2878,6 +2878,48 @@ static int mptcp_setsockopt_v6(struct mptcp_sock *msk, 
int optname,
        return ret;
 }
 
+static bool mptcp_unsupported(int level, int optname)
+{
+       if (level == SOL_IP) {
+               switch (optname) {
+               case IP_ADD_MEMBERSHIP:
+               case IP_ADD_SOURCE_MEMBERSHIP:
+               case IP_DROP_MEMBERSHIP:
+               case IP_DROP_SOURCE_MEMBERSHIP:
+               case IP_BLOCK_SOURCE:
+               case IP_UNBLOCK_SOURCE:
+               case MCAST_JOIN_GROUP:
+               case MCAST_LEAVE_GROUP:
+               case MCAST_JOIN_SOURCE_GROUP:
+               case MCAST_LEAVE_SOURCE_GROUP:
+               case MCAST_BLOCK_SOURCE:
+               case MCAST_UNBLOCK_SOURCE:
+               case MCAST_MSFILTER:
+                       return true;
+               }
+               return false;
+       }
+       if (level == SOL_IPV6) {
+               switch (optname) {
+               case IPV6_ADDRFORM:
+               case IPV6_ADD_MEMBERSHIP:
+               case IPV6_DROP_MEMBERSHIP:
+               case IPV6_JOIN_ANYCAST:
+               case IPV6_LEAVE_ANYCAST:
+               case MCAST_JOIN_GROUP:
+               case MCAST_LEAVE_GROUP:
+               case MCAST_JOIN_SOURCE_GROUP:
+               case MCAST_LEAVE_SOURCE_GROUP:
+               case MCAST_BLOCK_SOURCE:
+               case MCAST_UNBLOCK_SOURCE:
+               case MCAST_MSFILTER:
+                       return true;
+               }
+               return false;
+       }
+       return false;
+}
+
 static int mptcp_setsockopt(struct sock *sk, int level, int optname,
                            sockptr_t optval, unsigned int optlen)
 {
@@ -2886,6 +2928,9 @@ static int mptcp_setsockopt(struct sock *sk, int level, 
int optname,
 
        pr_debug("msk=%p", msk);
 
+       if (mptcp_unsupported(level, optname))
+               return -ENOPROTOOPT;
+
        if (level == SOL_SOCKET)
                return mptcp_setsockopt_sol_socket(msk, optname, optval, 
optlen);
 
-- 
2.26.2