Commit d6692b3b authored by Florian Westphal's avatar Florian Westphal Committed by Jakub Kicinski

mptcp: clear 'kern' flag from fallback sockets

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: cf7da0d6 ("mptcp: Create SUBFLOW socket for incoming connections")
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 404cd9a2
......@@ -2879,7 +2879,7 @@ 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 */
......@@ -2891,6 +2891,8 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
}
out:
newsk->sk_kern_sock = kern;
return newsk;
}
......
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