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tcp: ensure proper barriers in lockless contexts 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
include/net/sock.h
View File

@ -2226,6 +2226,31 @@ static inline bool sk_listener(const struct sock *sk)
return (1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV); return (1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV);
} }
/**
* sk_state_load - read sk->sk_state for lockless contexts
* @sk: socket pointer
*
* Paired with sk_state_store(). Used in places we do not hold socket lock :
* tcp_diag_get_info(), tcp_get_info(), tcp_poll(), get_tcp4_sock() ...
*/
static inline int sk_state_load(const struct sock *sk)
{
return smp_load_acquire(&sk->sk_state);
}
/**
* sk_state_store - update sk->sk_state
* @sk: socket pointer
* @newstate: new state
*
* Paired with sk_state_load(). Should be used in contexts where
* state change might impact lockless readers.
*/
static inline void sk_state_store(struct sock *sk, int newstate)
{
smp_store_release(&sk->sk_state, newstate);
}
void sock_enable_timestamp(struct sock *sk, int flag); void sock_enable_timestamp(struct sock *sk, int flag);
int sock_get_timestamp(struct sock *, struct timeval __user *); int sock_get_timestamp(struct sock *, struct timeval __user *);
int sock_get_timestampns(struct sock *, struct timespec __user *); int sock_get_timestampns(struct sock *, struct timespec __user *);

4
net/ipv4/inet_connection_sock.c
View File

@ -563,7 +563,7 @@ static void reqsk_timer_handler(unsigned long data)
int max_retries, thresh; int max_retries, thresh;
u8 defer_accept; u8 defer_accept;
if (sk_listener->sk_state != TCP_LISTEN) if (sk_state_load(sk_listener) != TCP_LISTEN)
goto drop; goto drop;
max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries; max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
@ -749,7 +749,7 @@ int inet_csk_listen_start(struct sock *sk, int backlog)
* It is OK, because this socket enters to hash table only * It is OK, because this socket enters to hash table only
* after validation is complete. * after validation is complete.
*/ */
sk->sk_state = TCP_LISTEN; sk_state_store(sk, TCP_LISTEN);
if (!sk->sk_prot->get_port(sk, inet->inet_num)) { if (!sk->sk_prot->get_port(sk, inet->inet_num)) {
inet->inet_sport = htons(inet->inet_num); inet->inet_sport = htons(inet->inet_num);

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; unsigned int mask;
struct sock *sk = sock->sk; struct sock *sk = sock->sk;
const struct tcp_sock *tp = tcp_sk(sk); const struct tcp_sock *tp = tcp_sk(sk);
int state;
sock_rps_record_flow(sk); sock_rps_record_flow(sk);
sock_poll_wait(file, sk_sleep(sk), wait); 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); return inet_csk_listen_poll(sk);
/* Socket is not locked. We are protected from async events /* 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 * NOTE. Check for TCP_CLOSE is added. The goal is to prevent
* blocking on fresh not-connected or disconnected socket. --ANK * 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; mask |= POLLHUP;
if (sk->sk_shutdown & RCV_SHUTDOWN) if (sk->sk_shutdown & RCV_SHUTDOWN)
mask |= POLLIN | POLLRDNORM | POLLRDHUP; mask |= POLLIN | POLLRDNORM | POLLRDHUP;
/* Connected or passive Fast Open socket? */ /* Connected or passive Fast Open socket? */
if (sk->sk_state != TCP_SYN_SENT && if (state != TCP_SYN_SENT &&
(sk->sk_state != TCP_SYN_RECV || tp->fastopen_rsk)) { (state != TCP_SYN_RECV || tp->fastopen_rsk)) {
int target = sock_rcvlowat(sk, 0, INT_MAX); int target = sock_rcvlowat(sk, 0, INT_MAX);
if (tp->urg_seq == tp->copied_seq && 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) tp->urg_data)
target++; 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) if (tp->rcv_nxt - tp->copied_seq >= target)
mask |= POLLIN | POLLRDNORM; 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 /* Change state AFTER socket is unhashed to avoid closed
* socket sitting in hash tables. * socket sitting in hash tables.
*/ */
sk->sk_state = state; sk_state_store(sk, state);
#ifdef STATE_TRACE #ifdef STATE_TRACE
SOCK_DEBUG(sk, "TCP sk=%p, State %s -> %s\n", sk, statename[oldstate], statename[state]); 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) if (sk->sk_type != SOCK_STREAM)
return; return;
info->tcpi_state = sk->sk_state; info->tcpi_state = sk_state_load(sk);
info->tcpi_ca_state = icsk->icsk_ca_state; info->tcpi_ca_state = icsk->icsk_ca_state;
info->tcpi_retransmits = icsk->icsk_retransmits; info->tcpi_retransmits = icsk->icsk_retransmits;
info->tcpi_probes = icsk->icsk_probes_out; 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_snd_mss = tp->mss_cache;
info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss; 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_unacked = sk->sk_ack_backlog;
info->tcpi_sacked = sk->sk_max_ack_backlog; info->tcpi_sacked = sk->sk_max_ack_backlog;
} else { } else {

2
net/ipv4/tcp_diag.c
View File

@ -21,7 +21,7 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
{ {
struct tcp_info *info = _info; struct tcp_info *info = _info;
if (sk->sk_state == TCP_LISTEN) { if (sk_state_load(sk) == TCP_LISTEN) {
r->idiag_rqueue = sk->sk_ack_backlog; r->idiag_rqueue = sk->sk_ack_backlog;
r->idiag_wqueue = sk->sk_max_ack_backlog; r->idiag_wqueue = sk->sk_max_ack_backlog;
} else if (sk->sk_type == SOCK_STREAM) { } else if (sk->sk_type == SOCK_STREAM) {

14
net/ipv4/tcp_ipv4.c
View File

@ -2158,6 +2158,7 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
__u16 destp = ntohs(inet->inet_dport); __u16 destp = ntohs(inet->inet_dport);
__u16 srcp = ntohs(inet->inet_sport); __u16 srcp = ntohs(inet->inet_sport);
int rx_queue; int rx_queue;
int state;
if (icsk->icsk_pending == ICSK_TIME_RETRANS || if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
@ -2175,17 +2176,18 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
timer_expires = jiffies; timer_expires = jiffies;
} }
if (sk->sk_state == TCP_LISTEN) state = sk_state_load(sk);
if (state == TCP_LISTEN)
rx_queue = sk->sk_ack_backlog; rx_queue = sk->sk_ack_backlog;
else else
/* /* Because we don't lock the socket,
* because we dont lock socket, we might find a transient negative value * we might find a transient negative value.
*/ */
rx_queue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0); rx_queue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0);
seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX " seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX "
"%08X %5u %8d %lu %d %pK %lu %lu %u %u %d", "%08X %5u %8d %lu %d %pK %lu %lu %u %u %d",
i, src, srcp, dest, destp, sk->sk_state, i, src, srcp, dest, destp, state,
tp->write_seq - tp->snd_una, tp->write_seq - tp->snd_una,
rx_queue, rx_queue,
timer_active, timer_active,
@ -2199,8 +2201,8 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
jiffies_to_clock_t(icsk->icsk_ack.ato), jiffies_to_clock_t(icsk->icsk_ack.ato),
(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong, (icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
tp->snd_cwnd, tp->snd_cwnd,
sk->sk_state == TCP_LISTEN ? state == TCP_LISTEN ?
(fastopenq ? fastopenq->max_qlen : 0) : fastopenq->max_qlen :
(tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh)); (tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh));
} }

19
net/ipv6/tcp_ipv6.c
View File

@ -1690,6 +1690,8 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
const struct tcp_sock *tp = tcp_sk(sp); const struct tcp_sock *tp = tcp_sk(sp);
const struct inet_connection_sock *icsk = inet_csk(sp); const struct inet_connection_sock *icsk = inet_csk(sp);
const struct fastopen_queue *fastopenq = &icsk->icsk_accept_queue.fastopenq; const struct fastopen_queue *fastopenq = &icsk->icsk_accept_queue.fastopenq;
int rx_queue;
int state;
dest = &sp->sk_v6_daddr; dest = &sp->sk_v6_daddr;
src = &sp->sk_v6_rcv_saddr; src = &sp->sk_v6_rcv_saddr;
@ -1710,6 +1712,15 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
timer_expires = jiffies; timer_expires = jiffies;
} }
state = sk_state_load(sp);
if (state == TCP_LISTEN)
rx_queue = sp->sk_ack_backlog;
else
/* Because we don't lock the socket,
* we might find a transient negative value.
*/
rx_queue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0);
seq_printf(seq, seq_printf(seq,
"%4d: %08X%08X%08X%08X:%04X %08X%08X%08X%08X:%04X " "%4d: %08X%08X%08X%08X:%04X %08X%08X%08X%08X:%04X "
"%02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %lu %lu %u %u %d\n", "%02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %lu %lu %u %u %d\n",
@ -1718,9 +1729,9 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
src->s6_addr32[2], src->s6_addr32[3], srcp, src->s6_addr32[2], src->s6_addr32[3], srcp,
dest->s6_addr32[0], dest->s6_addr32[1], dest->s6_addr32[0], dest->s6_addr32[1],
dest->s6_addr32[2], dest->s6_addr32[3], destp, dest->s6_addr32[2], dest->s6_addr32[3], destp,
sp->sk_state, state,
tp->write_seq-tp->snd_una, tp->write_seq - tp->snd_una,
(sp->sk_state == TCP_LISTEN) ? sp->sk_ack_backlog : (tp->rcv_nxt - tp->copied_seq), rx_queue,
timer_active, timer_active,
jiffies_delta_to_clock_t(timer_expires - jiffies), jiffies_delta_to_clock_t(timer_expires - jiffies),
icsk->icsk_retransmits, icsk->icsk_retransmits,
@ -1732,7 +1743,7 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
jiffies_to_clock_t(icsk->icsk_ack.ato), jiffies_to_clock_t(icsk->icsk_ack.ato),
(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong, (icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
tp->snd_cwnd, tp->snd_cwnd,
sp->sk_state == TCP_LISTEN ? state == TCP_LISTEN ?
fastopenq->max_qlen : fastopenq->max_qlen :
(tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh) (tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh)
); );