From: Florian Westphal <fw@strlen.de>
Date: Tue, 14 Dec 2021 23:16:02 +0000 (-0800)
Subject: mptcp: clear 'kern' flag from fallback sockets
X-Git-Tag: accepted/tizen/unified/20230118.172025~4143
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c26ac0ea3a91c210cf90452e625dc441adf3e549;p=platform%2Fkernel%2Flinux-rpi.git

mptcp: clear 'kern' flag from fallback sockets

[ Upstream commit d6692b3b97bdc165d150f4c1505751a323a80717 ]

The mptcp ULP extension relies on sk->sk_sock_kern being set correctly:
It prevents setsockopt(fd, IPPROTO_TCP, TCP_ULP, "mptcp", 6); from
working for plain tcp sockets (any userspace-exposed socket).

But in case of fallback, accept() can return a plain tcp sk.
In such case, sk is still tagged as 'kernel' and setsockopt will work.

This will crash the kernel, The subflow extension has a NULL ctx->conn
mptcp socket:

BUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0
Call Trace:
 tcp_data_ready+0xf8/0x370
 [..]

Fixes: cf7da0d66cc1 ("mptcp: Create SUBFLOW socket for incoming connections")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 421fa62..fdff811 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2901,7 +2901,7 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
 		 */
 		if (WARN_ON_ONCE(!new_mptcp_sock)) {
 			tcp_sk(newsk)->is_mptcp = 0;
-			return newsk;
+			goto out;
 		}
 
 		/* acquire the 2nd reference for the owning socket */
@@ -2913,6 +2913,8 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
 				MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
 	}
 
+out:
+	newsk->sk_kern_sock = kern;
 	return newsk;
 }