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net-timestamp: convert sk->sk_tskey to atomic_t
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UDP sendmsg() can be lockless, this is causing all kinds
of data races.

This patch converts sk->sk_tskey to remove one of these races.

BUG: KCSAN: data-race in __ip_append_data / __ip_append_data

read to 0xffff8881035d4b6c of 4 bytes by task 8877 on cpu 1:
 __ip_append_data+0x1c1/0x1de0 net/ipv4/ip_output.c:994
 ip_make_skb+0x13f/0x2d0 net/ipv4/ip_output.c:1636
 udp_sendmsg+0x12bd/0x14c0 net/ipv4/udp.c:1249
 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:819
 sock_sendmsg_nosec net/socket.c:705 [inline]
 sock_sendmsg net/socket.c:725 [inline]
 ____sys_sendmsg+0x39a/0x510 net/socket.c:2413
 ___sys_sendmsg net/socket.c:2467 [inline]
 __sys_sendmmsg+0x267/0x4c0 net/socket.c:2553
 __do_sys_sendmmsg net/socket.c:2582 [inline]
 __se_sys_sendmmsg net/socket.c:2579 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2579
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

write to 0xffff8881035d4b6c of 4 bytes by task 8880 on cpu 0:
 __ip_append_data+0x1d8/0x1de0 net/ipv4/ip_output.c:994
 ip_make_skb+0x13f/0x2d0 net/ipv4/ip_output.c:1636
 udp_sendmsg+0x12bd/0x14c0 net/ipv4/udp.c:1249
 inet_sendmsg+0x5f/0x80 net/ipv4/af_inet.c:819
 sock_sendmsg_nosec net/socket.c:705 [inline]
 sock_sendmsg net/socket.c:725 [inline]
 ____sys_sendmsg+0x39a/0x510 net/socket.c:2413
 ___sys_sendmsg net/socket.c:2467 [inline]
 __sys_sendmmsg+0x267/0x4c0 net/socket.c:2553
 __do_sys_sendmmsg net/socket.c:2582 [inline]
 __se_sys_sendmmsg net/socket.c:2579 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2579
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000054d -> 0x0000054e

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8880 Comm: syz-executor.5 Not tainted 5.17.0-rc2-syzkaller-00167-gdcb85f85fa6f-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: 09c2d25 ("net-timestamp: add key to disambiguate concurrent datagrams")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@davem330
Eric Dumazet authored and davem330 committed Feb 18, 2022
1 parent e9da0b5 commit a1cdec5
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Showing 6 changed files with 8 additions and 8 deletions.
4 changes: 2 additions & 2 deletions include/net/sock.h
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Original file line number Diff line number Diff line change
Expand Up @@ -507,7 +507,7 @@ struct sock {
#endif
u16 sk_tsflags;
u8 sk_shutdown;
u32 sk_tskey;
atomic_t sk_tskey;
atomic_t sk_zckey;

u8 sk_clockid;
Expand Down Expand Up @@ -2667,7 +2667,7 @@ static inline void _sock_tx_timestamp(struct sock *sk, __u16 tsflags,
__sock_tx_timestamp(tsflags, tx_flags);
if (tsflags & SOF_TIMESTAMPING_OPT_ID && tskey &&
tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
*tskey = sk->sk_tskey++;
*tskey = atomic_inc_return(&sk->sk_tskey) - 1;
}
if (unlikely(sock_flag(sk, SOCK_WIFI_STATUS)))
*tx_flags |= SKBTX_WIFI_STATUS;
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2 changes: 1 addition & 1 deletion net/can/j1939/transport.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2006,7 +2006,7 @@ struct j1939_session *j1939_tp_send(struct j1939_priv *priv,
/* set the end-packet for broadcast */
session->pkt.last = session->pkt.total;

skcb->tskey = session->sk->sk_tskey++;
skcb->tskey = atomic_inc_return(&session->sk->sk_tskey) - 1;
session->tskey = skcb->tskey;

return session;
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2 changes: 1 addition & 1 deletion net/core/skbuff.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4730,7 +4730,7 @@ static void __skb_complete_tx_timestamp(struct sk_buff *skb,
if (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID) {
serr->ee.ee_data = skb_shinfo(skb)->tskey;
if (sk_is_tcp(sk))
serr->ee.ee_data -= sk->sk_tskey;
serr->ee.ee_data -= atomic_read(&sk->sk_tskey);
}

err = sock_queue_err_skb(sk, skb);
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4 changes: 2 additions & 2 deletions net/core/sock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -879,9 +879,9 @@ int sock_set_timestamping(struct sock *sk, int optname,
if ((1 << sk->sk_state) &
(TCPF_CLOSE | TCPF_LISTEN))
return -EINVAL;
sk->sk_tskey = tcp_sk(sk)->snd_una;
atomic_set(&sk->sk_tskey, tcp_sk(sk)->snd_una);
} else {
sk->sk_tskey = 0;
atomic_set(&sk->sk_tskey, 0);
}
}

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2 changes: 1 addition & 1 deletion net/ipv4/ip_output.c
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Original file line number Diff line number Diff line change
Expand Up @@ -991,7 +991,7 @@ static int __ip_append_data(struct sock *sk,

if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
tskey = sk->sk_tskey++;
tskey = atomic_inc_return(&sk->sk_tskey) - 1;

hh_len = LL_RESERVED_SPACE(rt->dst.dev);

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2 changes: 1 addition & 1 deletion net/ipv6/ip6_output.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1465,7 +1465,7 @@ static int __ip6_append_data(struct sock *sk,

if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
tskey = sk->sk_tskey++;
tskey = atomic_inc_return(&sk->sk_tskey) - 1;

hh_len = LL_RESERVED_SPACE(rt->dst.dev);

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