dccp: fix data-race around dp->dccps_mss_cache

dccp_sendmsg() reads dp->dccps_mss_cache before locking the socket.
Same thing in do_dccp_getsockopt().

Add READ_ONCE()/WRITE_ONCE() annotations,
and change dccp_sendmsg() to check again dccps_mss_cache
after socket is locked.

Fixes: 7c657876b63c ("[DCCP]: Initial implementation")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230803163021.2958262-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/dccp/output.c b/net/dccp/output.c
index b8a2473..fd2eb14 100644 (file)
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -187,7 +187,7 @@ unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
 
        /* And store cached results */
        icsk->icsk_pmtu_cookie = pmtu;
-       dp->dccps_mss_cache = cur_mps;
+       WRITE_ONCE(dp->dccps_mss_cache, cur_mps);
 
        return cur_mps;
 }

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index f331e59..4e3266e 100644 (file)
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -630,7 +630,7 @@ static int do_dccp_getsockopt(struct sock *sk, int level, int optname,
                return dccp_getsockopt_service(sk, len,
                                               (__be32 __user *)optval, optlen);
        case DCCP_SOCKOPT_GET_CUR_MPS:
-               val = dp->dccps_mss_cache;
+               val = READ_ONCE(dp->dccps_mss_cache);
                break;
        case DCCP_SOCKOPT_AVAILABLE_CCIDS:
                return ccid_getsockopt_builtin_ccids(sk, len, optval, optlen);
@@ -739,7 +739,7 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
        trace_dccp_probe(sk, len);
 
-       if (len > dp->dccps_mss_cache)
+       if (len > READ_ONCE(dp->dccps_mss_cache))
                return -EMSGSIZE;
 
        lock_sock(sk);
@@ -772,6 +772,12 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
                goto out_discard;
        }
 
+       /* We need to check dccps_mss_cache after socket is locked. */
+       if (len > dp->dccps_mss_cache) {
+               rc = -EMSGSIZE;
+               goto out_discard;
+       }
+
        skb_reserve(skb, sk->sk_prot->max_header);
        rc = memcpy_from_msg(skb_put(skb, len), msg, len);
        if (rc != 0)