From 67eebc7a9217f999b779d46fba5312a716f0dc1d Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 3 Aug 2023 16:30:21 +0000
Subject: [PATCH] dccp: fix data-race around dp->dccps_mss_cache
commit a47e598fbd8617967e49d85c49c22f9fc642704c upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/dccp/output.c | 2 +-
net/dccp/proto.c | 10 ++++++++--
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/net/dccp/output.c b/net/dccp/output.c
index 6433187a5cc4..7490b4f09bbb 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -185,7 +185,7 @@ 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 3a3a2e1800be..cd868556452e 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -644,7 +644,7 @@ 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);
@@ -766,7 +766,7 @@ 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);
@@ -799,6 +799,12 @@ 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)