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Date: Mon, 23 Jan 2023 01:21:20 +0300
From: Kirill Tkhai <tkhai@...ru>
To: Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, kuniyu@...zon.com, gorcunov@...il.com,
tkhai@...ru
Subject: [PATCH net-next] unix: Guarantee sk_state relevance in case of it was
assigned by a task on other cpu
Some functions use unlocked check for sock::sk_state. This does not guarantee
a new value assigned to sk_state on some CPU is already visible on this CPU.
Example:
[CPU0:Task0] [CPU1:Task1]
unix_listen()
unix_state_lock(sk);
sk->sk_state = TCP_LISTEN;
unix_state_unlock(sk);
unix_accept()
if (sk->sk_state != TCP_LISTEN) /* not visible */
goto out; /* return error */
Task1 may miss new sk->sk_state value, and then unix_accept() returns error.
Since in this situation unix_accept() is called chronologically later, such
behavior is not obvious and it is wrong.
This patch aims to fix the problem. A new function unix_sock_state() is
introduced, and it makes sure a user never misses a new state assigned just
before the function is called. We will use it in the places, where unlocked
sk_state dereferencing was used before.
Note, that there remain some more places with sk_state unfixed. Also, the same
problem is with unix_peer(). This will be a subject for future patches.
Signed-off-by: Kirill Tkhai <tkhai@...ru>
---
net/unix/af_unix.c | 43 +++++++++++++++++++++++++++++++------------
1 file changed, 31 insertions(+), 12 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 009616fa0256..f53e09a0753b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -247,6 +247,28 @@ struct sock *unix_peer_get(struct sock *s)
}
EXPORT_SYMBOL_GPL(unix_peer_get);
+/* This function returns current sk->sk_state guaranteeing
+ * its relevance in case of assignment was made on other CPU.
+ */
+static unsigned char unix_sock_state(struct sock *sk)
+{
+ unsigned char s_state = READ_ONCE(sk->sk_state);
+
+ /* SOCK_STREAM and SOCK_SEQPACKET sockets never change their
+ * sk_state after switching to TCP_ESTABLISHED or TCP_LISTEN.
+ * We may avoid taking the lock in case of those states are
+ * already visible.
+ */
+ if ((s_state == TCP_ESTABLISHED || s_state == TCP_LISTEN)
+ && sk->sk_type != SOCK_DGRAM)
+ return s_state;
+
+ unix_state_lock(sk);
+ s_state = sk->sk_state;
+ unix_state_unlock(sk);
+ return s_state;
+}
+
static struct unix_address *unix_create_addr(struct sockaddr_un *sunaddr,
int addr_len)
{
@@ -812,13 +834,9 @@ static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
int nr_fds = 0;
if (sk) {
- s_state = READ_ONCE(sk->sk_state);
+ s_state = unix_sock_state(sk);
u = unix_sk(sk);
- /* SOCK_STREAM and SOCK_SEQPACKET sockets never change their
- * sk_state after switching to TCP_ESTABLISHED or TCP_LISTEN.
- * SOCK_DGRAM is ordinary. So, no lock is needed.
- */
if (sock->type == SOCK_DGRAM || s_state == TCP_ESTABLISHED)
nr_fds = atomic_read(&u->scm_stat.nr_fds);
else if (s_state == TCP_LISTEN)
@@ -1686,7 +1704,7 @@ static int unix_accept(struct socket *sock, struct socket *newsock, int flags,
goto out;
err = -EINVAL;
- if (sk->sk_state != TCP_LISTEN)
+ if (unix_sock_state(sk) != TCP_LISTEN)
goto out;
/* If socket state is TCP_LISTEN it cannot change (for now...),
@@ -2178,7 +2196,8 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
}
if (msg->msg_namelen) {
- err = sk->sk_state == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
+ unsigned char s_state = unix_sock_state(sk);
+ err = s_state == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
goto out_err;
} else {
err = -ENOTCONN;
@@ -2279,7 +2298,7 @@ static ssize_t unix_stream_sendpage(struct socket *socket, struct page *page,
return -EOPNOTSUPP;
other = unix_peer(sk);
- if (!other || sk->sk_state != TCP_ESTABLISHED)
+ if (!other || unix_sock_state(sk) != TCP_ESTABLISHED)
return -ENOTCONN;
if (false) {
@@ -2391,7 +2410,7 @@ static int unix_seqpacket_sendmsg(struct socket *sock, struct msghdr *msg,
if (err)
return err;
- if (sk->sk_state != TCP_ESTABLISHED)
+ if (unix_sock_state(sk) != TCP_ESTABLISHED)
return -ENOTCONN;
if (msg->msg_namelen)
@@ -2405,7 +2424,7 @@ static int unix_seqpacket_recvmsg(struct socket *sock, struct msghdr *msg,
{
struct sock *sk = sock->sk;
- if (sk->sk_state != TCP_ESTABLISHED)
+ if (unix_sock_state(sk) != TCP_ESTABLISHED)
return -ENOTCONN;
return unix_dgram_recvmsg(sock, msg, size, flags);
@@ -2689,7 +2708,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
{
- if (unlikely(sk->sk_state != TCP_ESTABLISHED))
+ if (unlikely(unix_sock_state(sk) != TCP_ESTABLISHED))
return -ENOTCONN;
return unix_read_skb(sk, recv_actor);
@@ -2713,7 +2732,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
size_t size = state->size;
unsigned int last_len;
- if (unlikely(sk->sk_state != TCP_ESTABLISHED)) {
+ if (unlikely(unix_sock_state(sk) != TCP_ESTABLISHED)) {
err = -EINVAL;
goto out;
}
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