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Commit 323f0968 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
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af_unix: fix races in sk_peer_pid and sk_peer_cred accesses 



commit 35306eb23814444bd4021f8a1c3047d3cb0c8b2b upstream.

Jann Horn reported that SO_PEERCRED and SO_PEERGROUPS implementations
are racy, as af_unix can concurrently change sk_peer_pid and sk_peer_cred.

In order to fix this issue, this patch adds a new spinlock that needs
to be used whenever these fields are read or written.

Jann also pointed out that l2cap_sock_get_peer_pid_cb() is currently
reading sk->sk_peer_pid which makes no sense, as this field
is only possibly set by AF_UNIX sockets.
We will have to clean this in a separate patch.
This could be done by reverting b48596d1dc25 "Bluetooth: L2CAP: Add get_peer_pid callback"
or implementing what was truly expected.

Fixes: 109f6e39 ("af_unix: Allow SO_PEERCRED to work across namespaces.")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarJann Horn <jannh@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Cc: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
[backport note: 4.4 and 4.9 don't have SO_PEERGROUPS, only SO_PEERCRED]
[backport note: got rid of sk_get_peer_cred(), no users in 4.4/4.9]
Signed-off-by: default avatarJann Horn <jannh@google.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a123b2f4

include/net/sock.h

+2 −0
Original line number Diff line number Diff line
@@ -429,8 +429,10 @@ struct sock { 
#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)

	__u32			sk_cgrp_prioidx;

#endif

	spinlock_t		sk_peer_lock;

	struct pid		*sk_peer_pid;

	const struct cred	*sk_peer_cred;



	long			sk_rcvtimeo;

	long			sk_sndtimeo;

	struct timer_list	sk_timer;

net/core/sock.c

+9 −3
Original line number Diff line number Diff line
@@ -1014,7 +1014,6 @@ set_rcvbuf: 
}

EXPORT_SYMBOL(sock_setsockopt);





static void cred_to_ucred(struct pid *pid, const struct cred *cred,

			  struct ucred *ucred)

{
@@ -1174,7 +1173,11 @@ int sock_getsockopt(struct socket *sock, int level, int optname, 
		struct ucred peercred;

		if (len > sizeof(peercred))

			len = sizeof(peercred);



		spin_lock(&sk->sk_peer_lock);

		cred_to_ucred(sk->sk_peer_pid, sk->sk_peer_cred, &peercred);

		spin_unlock(&sk->sk_peer_lock);



		if (copy_to_user(optval, &peercred, len))

			return -EFAULT;

		goto lenout;
@@ -1467,9 +1470,10 @@ void sk_destruct(struct sock *sk) 
		sk->sk_frag.page = NULL;

	}



	if (sk->sk_peer_cred)

	/* We do not need to acquire sk->sk_peer_lock, we are the last user. */

	put_cred(sk->sk_peer_cred);

	put_pid(sk->sk_peer_pid);



	if (likely(sk->sk_net_refcnt))

		put_net(sock_net(sk));

	sk_prot_free(sk->sk_prot_creator, sk);
@@ -2442,6 +2446,8 @@ void sock_init_data(struct socket *sock, struct sock *sk) 


	sk->sk_peer_pid 	=	NULL;

	sk->sk_peer_cred	=	NULL;

	spin_lock_init(&sk->sk_peer_lock);



	sk->sk_write_pending	=	0;

	sk->sk_rcvlowat		=	1;

	sk->sk_rcvtimeo		=	MAX_SCHEDULE_TIMEOUT;

net/unix/af_unix.c

+28 −6
Original line number Diff line number Diff line
@@ -594,20 +594,42 @@ static void unix_release_sock(struct sock *sk, int embrion) 


static void init_peercred(struct sock *sk)

{

	put_pid(sk->sk_peer_pid);

	if (sk->sk_peer_cred)

		put_cred(sk->sk_peer_cred);

	const struct cred *old_cred;

	struct pid *old_pid;



	spin_lock(&sk->sk_peer_lock);

	old_pid = sk->sk_peer_pid;

	old_cred = sk->sk_peer_cred;

	sk->sk_peer_pid  = get_pid(task_tgid(current));

	sk->sk_peer_cred = get_current_cred();

	spin_unlock(&sk->sk_peer_lock);



	put_pid(old_pid);

	put_cred(old_cred);

}



static void copy_peercred(struct sock *sk, struct sock *peersk)

{

	put_pid(sk->sk_peer_pid);

	if (sk->sk_peer_cred)

		put_cred(sk->sk_peer_cred);

	const struct cred *old_cred;

	struct pid *old_pid;



	if (sk < peersk) {

		spin_lock(&sk->sk_peer_lock);

		spin_lock_nested(&peersk->sk_peer_lock, SINGLE_DEPTH_NESTING);

	} else {

		spin_lock(&peersk->sk_peer_lock);

		spin_lock_nested(&sk->sk_peer_lock, SINGLE_DEPTH_NESTING);

	}

	old_pid = sk->sk_peer_pid;

	old_cred = sk->sk_peer_cred;

	sk->sk_peer_pid  = get_pid(peersk->sk_peer_pid);

	sk->sk_peer_cred = get_cred(peersk->sk_peer_cred);



	spin_unlock(&sk->sk_peer_lock);

	spin_unlock(&peersk->sk_peer_lock);



	put_pid(old_pid);

	put_cred(old_cred);

}



static int unix_listen(struct socket *sock, int backlog)