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tcp: ensure proper barriers in lockless contexts

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Some functions access TCP sockets without holding a lock and
might output non consistent data, depending on compiler and or
architecture.

tcp_diag_get_info(), tcp_get_info(), tcp_poll(), get_tcp4_sock() ...

Introduce sk_state_load() and sk_state_store() to fix the issues,
and more clearly document where this lack of locking is happening.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2015-11-12 08:43:18 -08:00
committed by David S. Miller
parent 5883d9c6d7
commit 00fd38d938
6 changed files with 62 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
net/ipv4/tcp.c
View File

@@ -451,11 +451,14 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
unsigned int mask;
struct sock *sk = sock->sk;
const struct tcp_sock *tp = tcp_sk(sk);
int state;
sock_rps_record_flow(sk);
sock_poll_wait(file, sk_sleep(sk), wait);
if (sk->sk_state == TCP_LISTEN)
state = sk_state_load(sk);
if (state == TCP_LISTEN)
return inet_csk_listen_poll(sk);
/* Socket is not locked. We are protected from async events
@@ -492,14 +495,14 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
* NOTE. Check for TCP_CLOSE is added. The goal is to prevent
* blocking on fresh not-connected or disconnected socket. --ANK
*/
if (sk->sk_shutdown == SHUTDOWN_MASK || sk->sk_state == TCP_CLOSE)
if (sk->sk_shutdown == SHUTDOWN_MASK || state == TCP_CLOSE)
mask |= POLLHUP;
if (sk->sk_shutdown & RCV_SHUTDOWN)
mask |= POLLIN | POLLRDNORM | POLLRDHUP;
/* Connected or passive Fast Open socket? */
if (sk->sk_state != TCP_SYN_SENT &&
(sk->sk_state != TCP_SYN_RECV || tp->fastopen_rsk)) {
if (state != TCP_SYN_SENT &&
(state != TCP_SYN_RECV || tp->fastopen_rsk)) {
int target = sock_rcvlowat(sk, 0, INT_MAX);
if (tp->urg_seq == tp->copied_seq &&
@@ -507,9 +510,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
tp->urg_data)
target++;
/* Potential race condition. If read of tp below will
* escape above sk->sk_state, we can be illegally awaken
* in SYN_* states. */
if (tp->rcv_nxt - tp->copied_seq >= target)
mask |= POLLIN | POLLRDNORM;
@@ -1934,7 +1934,7 @@ void tcp_set_state(struct sock *sk, int state)
/* Change state AFTER socket is unhashed to avoid closed
* socket sitting in hash tables.
*/
sk->sk_state = state;
sk_state_store(sk, state);
#ifdef STATE_TRACE
SOCK_DEBUG(sk, "TCP sk=%p, State %s -> %s\n", sk, statename[oldstate], statename[state]);
@@ -2644,7 +2644,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
if (sk->sk_type != SOCK_STREAM)
return;
info->tcpi_state = sk->sk_state;
info->tcpi_state = sk_state_load(sk);
info->tcpi_ca_state = icsk->icsk_ca_state;
info->tcpi_retransmits = icsk->icsk_retransmits;
info->tcpi_probes = icsk->icsk_probes_out;
@@ -2672,7 +2673,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
info->tcpi_snd_mss = tp->mss_cache;
info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
if (sk->sk_state == TCP_LISTEN) {
if (info->tcpi_state == TCP_LISTEN) {
info->tcpi_unacked = sk->sk_ack_backlog;
info->tcpi_sacked = sk->sk_max_ack_backlog;
} else {