sock: Make sock->sk_stamp thread-safe

[ Upstream commit 3a0ed3e9619738067214871e9cb826fa23b2ddb9 ]

Al Viro mentioned (Message-ID
<20170626041334.GZ10672@ZenIV.linux.org.uk>)
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 9115e8cd2a0c ("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 <deepa.kernel@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/net/sock.h b/include/net/sock.h
index 577075713ad512b996a6091b612da213e9c5b283..7420299c31f57fe4c4c4171c5d47f0c26249526b 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -299,6 +299,7 @@ struct cg_proto;
   *    @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_socket: Identd and reporting IO signals
@@ -434,6 +435,9 @@ struct sock {
        long                    sk_sndtimeo;
        struct timer_list       sk_timer;
        ktime_t                 sk_stamp;
+#if BITS_PER_LONG==32
+       seqlock_t               sk_stamp_seq;
+#endif
        u16                     sk_tsflags;
        u32                     sk_tskey;
        struct socket           *sk_socket;
@@ -2146,6 +2150,34 @@ 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,
@@ -2170,7 +2202,7 @@ 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);
@@ -2190,7 +2222,7 @@ 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
-               sk->sk_stamp = skb->tstamp;
+               sock_write_timestamp(sk, skb->tstamp);
 }
 
 void __sock_tx_timestamp(const struct sock *sk, __u8 *tx_flags);

diff --git a/net/compat.c b/net/compat.c
index 17e97b106458c6e7e6087ddfa637610a8e75c807..d676840104556d59b2ec5cdf14523b810e9d377d 100644 (file)
--- a/net/compat.c
+++ b/net/compat.c
@@ -443,12 +443,14 @@ int compat_sock_get_timestamp(struct sock *sk, struct timeval __user *userstamp)
        err = -ENOENT;
        if (!sock_flag(sk, SOCK_TIMESTAMP))
                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) ||
@@ -471,12 +473,13 @@ int compat_sock_get_timestampns(struct sock *sk, struct timespec __user *usersta
        err = -ENOENT;
        if (!sock_flag(sk, SOCK_TIMESTAMP))
                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) ||

diff --git a/net/core/sock.c b/net/core/sock.c
index 4238835a0e4e80ddf2b1fe00606149784bab6817..9fb1c073d0c428a39b2812c7fe35fa72e0b4feb5 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2423,6 +2423,9 @@ void sock_init_data(struct socket *sock, struct sock *sk)
        sk->sk_sndtimeo         =       MAX_SCHEDULE_TIMEOUT;
 
        sk->sk_stamp = ktime_set(-1L, 0);
+#if BITS_PER_LONG==32
+       seqlock_init(&sk->sk_stamp_seq);
+#endif
 
 #ifdef CONFIG_NET_RX_BUSY_POLL
        sk->sk_napi_id          =       0;

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 1413cdcc131c4a7ed49487e4a19691644e0ca65c..9701fcca002c6b3efc0661467b21f1cd55baf8ac 100644 (file)
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -614,7 +614,7 @@ 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 - sizeof(struct udphdr);