[PATCH 4.4 34/73] af_unix: split u->readlock into two: iolock and bindlock

Greg Kroah-Hartman
2016-09-28T09:34:23Z

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 6e1ce3c3451291142a57c4f3f6f999a29fb5b3bc upstream.

Right now we use the 'readlock' both for protecting some of the af_unix
IO path and for making the bind be single-threaded.

The two are independent, but using the same lock makes for a nasty
deadlock due to ordering with regards to filesystem locking. The bind
locking would want to nest outside the VSF pathname locking, but the IO
locking wants to nest inside some of those same locks.

We tried to fix this earlier with commit c845acb324aa ("af_unix: Fix
splice-bind deadlock") which moved the readlock inside the vfs locks,
but that caused problems with overlayfs that will then call back into
filesystem routines that take the lock in the wrong order anyway.

Splitting the locks means that we can go back to having the bind lock be
the outermost lock, and we don't have any deadlocks with lock ordering.

Acked-by: Rainer Weikusat <rweikusat@cyberadapt.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/net/af_unix.h | 2 +-
net/unix/af_unix.c | 41 +++++++++++++++++++++--------------------
2 files changed, 22 insertions(+), 21 deletions(-)

--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -52,7 +52,7 @@ struct unix_sock {
struct sock sk;
struct unix_address *addr;
struct path path;
- struct mutex readlock;
+ struct mutex iolock, bindlock;
struct sock *peer;
struct list_head link;
atomic_long_t inflight;
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -661,11 +661,11 @@ static int unix_set_peek_off(struct sock
{
struct unix_sock *u = unix_sk(sk);

- if (mutex_lock_interruptible(&u->readlock))
+ if (mutex_lock_interruptible(&u->iolock))
return -EINTR;

sk->sk_peek_off = val;
- mutex_unlock(&u->readlock);
+ mutex_unlock(&u->iolock);

return 0;
}
@@ -778,7 +778,8 @@ static struct sock *unix_create1(struct
spin_lock_init(&u->lock);
atomic_long_set(&u->inflight, 0);
INIT_LIST_HEAD(&u->link);
- mutex_init(&u->readlock); /* single task reading lock */
+ mutex_init(&u->iolock); /* single task reading lock */
+ mutex_init(&u->bindlock); /* single task binding lock */
init_waitqueue_head(&u->peer_wait);
init_waitqueue_func_entry(&u->peer_wake, unix_dgram_peer_wake_relay);
unix_insert_socket(unix_sockets_unbound(sk), sk);
@@ -847,7 +848,7 @@ static int unix_autobind(struct socket *
int err;
unsigned int retries = 0;

- err = mutex_lock_interruptible(&u->readlock);
+ err = mutex_lock_interruptible(&u->bindlock);
if (err)
return err;

@@ -894,7 +895,7 @@ retry:
spin_unlock(&unix_table_lock);
err = 0;

-out: mutex_unlock(&u->readlock);
+out: mutex_unlock(&u->bindlock);
return err;
}

@@ -1008,7 +1009,7 @@ static int unix_bind(struct socket *sock
goto out;
addr_len = err;

- err = mutex_lock_interruptible(&u->readlock);
+ err = mutex_lock_interruptible(&u->bindlock);
if (err)
goto out;

@@ -1062,7 +1063,7 @@ static int unix_bind(struct socket *sock
out_unlock:
spin_unlock(&unix_table_lock);
out_up:
- mutex_unlock(&u->readlock);
+ mutex_unlock(&u->bindlock);
out:
return err;
}
@@ -1957,17 +1958,17 @@ static ssize_t unix_stream_sendpage(stru
if (false) {
alloc_skb:
unix_state_unlock(other);
- mutex_unlock(&unix_sk(other)->readlock);
+ mutex_unlock(&unix_sk(other)->iolock);
newskb = sock_alloc_send_pskb(sk, 0, 0, flags & MSG_DONTWAIT,
&err, 0);
if (!newskb)
goto err;
}

- /* we must acquire readlock as we modify already present
+ /* we must acquire iolock as we modify already present
* skbs in the sk_receive_queue and mess with skb->len
*/
- err = mutex_lock_interruptible(&unix_sk(other)->readlock);
+ err = mutex_lock_interruptible(&unix_sk(other)->iolock);
if (err) {
err = flags & MSG_DONTWAIT ? -EAGAIN : -ERESTARTSYS;
goto err;
@@ -2034,7 +2035,7 @@ alloc_skb:
}

unix_state_unlock(other);
- mutex_unlock(&unix_sk(other)->readlock);
+ mutex_unlock(&unix_sk(other)->iolock);

other->sk_data_ready(other);
scm_destroy(&scm);
@@ -2043,7 +2044,7 @@ alloc_skb:
err_state_unlock:
unix_state_unlock(other);
err_unlock:
- mutex_unlock(&unix_sk(other)->readlock);
+ mutex_unlock(&unix_sk(other)->iolock);
err:
kfree_skb(newskb);
if (send_sigpipe && !(flags & MSG_NOSIGNAL))
@@ -2108,7 +2109,7 @@ static int unix_dgram_recvmsg(struct soc
if (flags&MSG_OOB)
goto out;

- err = mutex_lock_interruptible(&u->readlock);
+ err = mutex_lock_interruptible(&u->iolock);
if (unlikely(err)) {
/* recvmsg() in non blocking mode is supposed to return -EAGAIN
* sk_rcvtimeo is not honored by mutex_lock_interruptible()
@@ -2184,7 +2185,7 @@ static int unix_dgram_recvmsg(struct soc
out_free:
skb_free_datagram(sk, skb);
out_unlock:
- mutex_unlock(&u->readlock);
+ mutex_unlock(&u->iolock);
out:
return err;
}
@@ -2279,7 +2280,7 @@ static int unix_stream_read_generic(stru
/* Lock the socket to prevent queue disordering
* while sleeps in memcpy_tomsg
*/
- mutex_lock(&u->readlock);
+ mutex_lock(&u->iolock);

if (flags & MSG_PEEK)
skip = sk_peek_offset(sk, flags);
@@ -2320,7 +2321,7 @@ again:
break;
}

- mutex_unlock(&u->readlock);
+ mutex_unlock(&u->iolock);

timeo = unix_stream_data_wait(sk, timeo, last,
last_len);
@@ -2331,7 +2332,7 @@ again:
goto out;
}

- mutex_lock(&u->readlock);
+ mutex_lock(&u->iolock);
continue;
unlock:
unix_state_unlock(sk);
@@ -2434,7 +2435,7 @@ unlock:
}
} while (size);

- mutex_unlock(&u->readlock);
+ mutex_unlock(&u->iolock);
if (state->msg)
scm_recv(sock, state->msg, &scm, flags);
else
@@ -2475,9 +2476,9 @@ static ssize_t skb_unix_socket_splice(st
int ret;
struct unix_sock *u = unix_sk(sk);

- mutex_unlock(&u->readlock);
+ mutex_unlock(&u->iolock);
ret = splice_to_pipe(pipe, spd);
- mutex_lock(&u->readlock);
+ mutex_lock(&u->iolock);

return ret;
}