From: Florian Westphal fw@strlen.de
[ 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 --- net/mptcp/protocol.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 421fa62ce5cdf..fdff811c9a0da 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; }