[PATCH net] tcp: tcp_get_info() should fetch socket fields once

[PATCH net] tcp: tcp_get_info() should fetch socket fields once

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

tcp_get_info() can be called without holding socket lock,
so any socket fields can change under us.

Use READ_ONCE() to fetch sk_pacing_rate and sk_max_pacing_rate

Fixes: 977cb0ecf82e ("tcp: add pacing_rate information into tcp_info")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
David, I do not think this needs stable backport, this is a quite
minor bug. I've added the 'Fixes' tag for reference only.

 net/ipv4/tcp.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 18e3a12eb1b2..59c8a027721b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2595,6 +2595,7 @@ void tcp_get_info(const struct sock *sk, struct tcp_info *info)
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	u32 now = tcp_time_stamp;
+	u32 rate;
 
 	memset(info, 0, sizeof(*info));
 
@@ -2655,10 +2656,11 @@ void tcp_get_info(const struct sock *sk, struct tcp_info *info)
 
 	info->tcpi_total_retrans = tp->total_retrans;
 
-	info->tcpi_pacing_rate = sk->sk_pacing_rate != ~0U ?
-					sk->sk_pacing_rate : ~0ULL;
-	info->tcpi_max_pacing_rate = sk->sk_max_pacing_rate != ~0U ?
-					sk->sk_max_pacing_rate : ~0ULL;
+	rate = READ_ONCE(sk->sk_pacing_rate);
+	info->tcpi_pacing_rate = rate != ~0U ? rate : ~0ULL;
+
+	rate = READ_ONCE(sk->sk_max_pacing_rate);
+	info->tcpi_max_pacing_rate = rate != ~0U ? rate : ~0ULL;
 }
 EXPORT_SYMBOL_GPL(tcp_get_info);
 

Re: [PATCH net] tcp: tcp_get_info() should fetch socket fields once

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 16 Apr 2015 16:12:28 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> tcp_get_info() can be called without holding socket lock,
> so any socket fields can change under us.
> 
> Use READ_ONCE() to fetch sk_pacing_rate and sk_max_pacing_rate
> 
> Fixes: 977cb0ecf82e ("tcp: add pacing_rate information into tcp_info")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
> David, I do not think this needs stable backport, this is a quite
> minor bug. I've added the 'Fixes' tag for reference only.

Ok, applied.