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sock: Make sock->sk_stamp thread-safe
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Al Viro mentioned (Message-ID
<[email protected]>)
that there is probably a race condition
lurking in accesses of sk_stamp on 32-bit machines.

sock->sk_stamp is of type ktime_t which is always an s64.
On a 32 bit architecture, we might run into situations of
unsafe access as the access to the field becomes non atomic.

Use seqlocks for synchronization.
This allows us to avoid using spinlocks for readers as
readers do not need mutual exclusion.

Another approach to solve this is to require sk_lock for all
modifications of the timestamps. The current approach allows
for timestamps to have their own lock: sk_stamp_lock.
This allows for the patch to not compete with already
existing critical sections, and side effects are limited
to the paths in the patch.

The addition of the new field maintains the data locality
optimizations from
commit 9115e8c ("net: reorganize struct sock for better data
locality")

Note that all the instances of the sk_stamp accesses
are either through the ioctl or the syscall recvmsg.

Signed-off-by: Deepa Dinamani <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@deepa-hub @davem330
deepa-hub authored and davem330 committed Jan 1, 2019
1 parent 756af9c commit 3a0ed3e
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Showing 4 changed files with 55 additions and 15 deletions.
38 changes: 35 additions & 3 deletions include/net/sock.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -298,6 +298,7 @@ struct sock_common {
* @sk_filter: socket filtering instructions
* @sk_timer: sock cleanup timer
* @sk_stamp: time stamp of last packet received
* @sk_stamp_seq: lock for accessing sk_stamp on 32 bit architectures only
* @sk_tsflags: SO_TIMESTAMPING socket options
* @sk_tskey: counter to disambiguate concurrent tstamp requests
* @sk_zckey: counter to order MSG_ZEROCOPY notifications
Expand Down Expand Up @@ -474,6 +475,9 @@ struct sock {
const struct cred *sk_peer_cred;
long sk_rcvtimeo;
ktime_t sk_stamp;
#if BITS_PER_LONG==32
seqlock_t sk_stamp_seq;
#endif
u16 sk_tsflags;
u8 sk_shutdown;
u32 sk_tskey;
Expand Down Expand Up @@ -2297,6 +2301,34 @@ static inline void sk_drops_add(struct sock *sk, const struct sk_buff *skb)
atomic_add(segs, &sk->sk_drops);
}

static inline ktime_t sock_read_timestamp(struct sock *sk)
{
#if BITS_PER_LONG==32
unsigned int seq;
ktime_t kt;

do {
seq = read_seqbegin(&sk->sk_stamp_seq);
kt = sk->sk_stamp;
} while (read_seqretry(&sk->sk_stamp_seq, seq));

return kt;
#else
return sk->sk_stamp;
#endif
}

static inline void sock_write_timestamp(struct sock *sk, ktime_t kt)
{
#if BITS_PER_LONG==32
write_seqlock(&sk->sk_stamp_seq);
sk->sk_stamp = kt;
write_sequnlock(&sk->sk_stamp_seq);
#else
sk->sk_stamp = kt;
#endif
}

void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
struct sk_buff *skb);
void __sock_recv_wifi_status(struct msghdr *msg, struct sock *sk,
Expand All @@ -2321,7 +2353,7 @@ sock_recv_timestamp(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
(sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE)))
__sock_recv_timestamp(msg, sk, skb);
else
sk->sk_stamp = kt;
sock_write_timestamp(sk, kt);

if (sock_flag(sk, SOCK_WIFI_STATUS) && skb->wifi_acked_valid)
__sock_recv_wifi_status(msg, sk, skb);
Expand All @@ -2342,9 +2374,9 @@ static inline void sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
if (sk->sk_flags & FLAGS_TS_OR_DROPS || sk->sk_tsflags & TSFLAGS_ANY)
__sock_recv_ts_and_drops(msg, sk, skb);
else if (unlikely(sock_flag(sk, SOCK_TIMESTAMP)))
sk->sk_stamp = skb->tstamp;
sock_write_timestamp(sk, skb->tstamp);
else if (unlikely(sk->sk_stamp == SK_DEFAULT_STAMP))
sk->sk_stamp = 0;
sock_write_timestamp(sk, 0);
}

void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags);
Expand Down
15 changes: 9 additions & 6 deletions net/compat.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -467,12 +467,14 @@ int compat_sock_get_timestamp(struct sock *sk, struct timeval __user *userstamp)
ctv = (struct compat_timeval __user *) userstamp;
err = -ENOENT;
sock_enable_timestamp(sk, SOCK_TIMESTAMP);
tv = ktime_to_timeval(sk->sk_stamp);
tv = ktime_to_timeval(sock_read_timestamp(sk));

if (tv.tv_sec == -1)
return err;
if (tv.tv_sec == 0) {
sk->sk_stamp = ktime_get_real();
tv = ktime_to_timeval(sk->sk_stamp);
ktime_t kt = ktime_get_real();
sock_write_timestamp(sk, kt);
tv = ktime_to_timeval(kt);
}
err = 0;
if (put_user(tv.tv_sec, &ctv->tv_sec) ||
Expand All @@ -494,12 +496,13 @@ int compat_sock_get_timestampns(struct sock *sk, struct timespec __user *usersta
ctv = (struct compat_timespec __user *) userstamp;
err = -ENOENT;
sock_enable_timestamp(sk, SOCK_TIMESTAMP);
ts = ktime_to_timespec(sk->sk_stamp);
ts = ktime_to_timespec(sock_read_timestamp(sk));
if (ts.tv_sec == -1)
return err;
if (ts.tv_sec == 0) {
sk->sk_stamp = ktime_get_real();
ts = ktime_to_timespec(sk->sk_stamp);
ktime_t kt = ktime_get_real();
sock_write_timestamp(sk, kt);
ts = ktime_to_timespec(kt);
}
err = 0;
if (put_user(ts.tv_sec, &ctv->tv_sec) ||
Expand Down
15 changes: 10 additions & 5 deletions net/core/sock.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2751,6 +2751,9 @@ void sock_init_data(struct socket *sock, struct sock *sk)
sk->sk_sndtimeo = MAX_SCHEDULE_TIMEOUT;

sk->sk_stamp = SK_DEFAULT_STAMP;
#if BITS_PER_LONG==32
seqlock_init(&sk->sk_stamp_seq);
#endif
atomic_set(&sk->sk_zckey, 0);

#ifdef CONFIG_NET_RX_BUSY_POLL
Expand Down Expand Up @@ -2850,12 +2853,13 @@ int sock_get_timestamp(struct sock *sk, struct timeval __user *userstamp)
struct timeval tv;

sock_enable_timestamp(sk, SOCK_TIMESTAMP);
tv = ktime_to_timeval(sk->sk_stamp);
tv = ktime_to_timeval(sock_read_timestamp(sk));
if (tv.tv_sec == -1)
return -ENOENT;
if (tv.tv_sec == 0) {
sk->sk_stamp = ktime_get_real();
tv = ktime_to_timeval(sk->sk_stamp);
ktime_t kt = ktime_get_real();
sock_write_timestamp(sk, kt);
tv = ktime_to_timeval(kt);
}
return copy_to_user(userstamp, &tv, sizeof(tv)) ? -EFAULT : 0;
}
Expand All @@ -2866,11 +2870,12 @@ int sock_get_timestampns(struct sock *sk, struct timespec __user *userstamp)
struct timespec ts;

sock_enable_timestamp(sk, SOCK_TIMESTAMP);
ts = ktime_to_timespec(sk->sk_stamp);
ts = ktime_to_timespec(sock_read_timestamp(sk));
if (ts.tv_sec == -1)
return -ENOENT;
if (ts.tv_sec == 0) {
sk->sk_stamp = ktime_get_real();
ktime_t kt = ktime_get_real();
sock_write_timestamp(sk, kt);
ts = ktime_to_timespec(sk->sk_stamp);
}
return copy_to_user(userstamp, &ts, sizeof(ts)) ? -EFAULT : 0;
Expand Down
2 changes: 1 addition & 1 deletion net/sunrpc/svcsock.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -549,7 +549,7 @@ static int svc_udp_recvfrom(struct svc_rqst *rqstp)
/* Don't enable netstamp, sunrpc doesn't
need that much accuracy */
}
svsk->sk_sk->sk_stamp = skb->tstamp;
sock_write_timestamp(svsk->sk_sk, skb->tstamp);
set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); /* there may be more data... */

len = skb->len;
Expand Down

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