Patchwork [net-next,1/2] ipv6: remove unnecessary codes in tcp_ipv6.c

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Submitter roy.qing.li@gmail.com
Date July 2, 2012, 3:18 a.m.
Message ID <1341199140-17135-1-git-send-email-roy.qing.li@gmail.com>
Download mbox | patch
Permalink /patch/168483/
State Accepted
Delegated to: David Miller
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Comments

roy.qing.li@gmail.com - July 2, 2012, 3:18 a.m.
From: RongQing.Li <roy.qing.li@gmail.com>

opt always equals np->opts, so it is meaningless to define opt, and
check if opt does not equal np->opts and then try to free opt.

Signed-off-by: RongQing.Li <roy.qing.li@gmail.com>
---
 net/ipv6/tcp_ipv6.c |   16 +++-------------
 1 files changed, 3 insertions(+), 13 deletions(-)
David Miller - July 2, 2012, 3:26 a.m.
From: roy.qing.li@gmail.com
Date: Mon,  2 Jul 2012 11:18:59 +0800

> -	if (opt) {
> -		newnp->opt = ipv6_dup_options(newsk, opt);
> -		if (opt != np->opt)
> -			sock_kfree_s(sk, opt, opt->tot_len);

This is bogus, if we copy the options into a new copy in
ipv6_dup_options() we have to free the old one or else we
leak it.
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roy.qing.li@gmail.com - July 2, 2012, 5:23 a.m.
2012/7/2 David Miller <davem@davemloft.net>:
> From: roy.qing.li@gmail.com
> Date: Mon,  2 Jul 2012 11:18:59 +0800
>
>> -     if (opt) {
>> -             newnp->opt = ipv6_dup_options(newsk, opt);
>> -             if (opt != np->opt)
>> -                     sock_kfree_s(sk, opt, opt->tot_len);
>
> This is bogus, if we copy the options into a new copy in
> ipv6_dup_options() we have to free the old one or else we
> leak it.

Do you mean I should free newnp->opt firstly ?

If I understand it right, I think we do not need to free it. the
process is below:

newsk = tcp_v4_syn_recv_sock(sk, skb, req, dst);
..
newnp = inet6_sk(newsk);
..
memcpy(newnp, np, sizeof(struct ipv6_pinfo));
..
newnp->opt         = NULL;

So newnp->opt is not a effective memory.


Thanks.
-Roy
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David Miller - July 2, 2012, 5:37 a.m.
From: RongQing Li <roy.qing.li@gmail.com>
Date: Mon, 2 Jul 2012 13:23:09 +0800

> 2012/7/2 David Miller <davem@davemloft.net>:
>> From: roy.qing.li@gmail.com
>> Date: Mon,  2 Jul 2012 11:18:59 +0800
>>
>>> -     if (opt) {
>>> -             newnp->opt = ipv6_dup_options(newsk, opt);
>>> -             if (opt != np->opt)
>>> -                     sock_kfree_s(sk, opt, opt->tot_len);
>>
>> This is bogus, if we copy the options into a new copy in
>> ipv6_dup_options() we have to free the old one or else we
>> leak it.
> 
> Do you mean I should free newnp->opt firstly ?
> 
> If I understand it right, I think we do not need to free it. the
> process is below:
> 
> newsk = tcp_v4_syn_recv_sock(sk, skb, req, dst);
> ..
> newnp = inet6_sk(newsk);
> ..
> memcpy(newnp, np, sizeof(struct ipv6_pinfo));
> ..
> newnp->opt         = NULL;
> 
> So newnp->opt is not a effective memory.

ipv6_dup_options() allocates new memory for the options and this call
statement assigns that new pointer to np->opt.

If you do not free the old (before ipv6_dup_options()) np->opt memory
here, it is lost forever.
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Eric Dumazet - July 2, 2012, 8:13 a.m.
On Sun, 2012-07-01 at 20:26 -0700, David Miller wrote:
> From: roy.qing.li@gmail.com
> Date: Mon,  2 Jul 2012 11:18:59 +0800
> 
> > -	if (opt) {
> > -		newnp->opt = ipv6_dup_options(newsk, opt);
> > -		if (opt != np->opt)
> > -			sock_kfree_s(sk, opt, opt->tot_len);
> 
> This is bogus, if we copy the options into a new copy in
> ipv6_dup_options() we have to free the old one or else we
> leak it.

Note that the old one is the np->opt of the listener, not the child.

I dont understand how np->opt could change under us, since we have
the listener socket locked.

If np->opt can change under us, we are doomed and need to add refcounts.




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Eric Dumazet - July 2, 2012, 8:54 a.m.
On Mon, 2012-07-02 at 10:13 +0200, Eric Dumazet wrote:

> Note that the old one is the np->opt of the listener, not the child.
> 
> I dont understand how np->opt could change under us, since we have
> the listener socket locked.
> 
> If np->opt can change under us, we are doomed and need to add refcounts.

Hmm, it seems net/ipv6/udp.c uses np->opt outside of the
lock_sock()/release_sock(sk) boundary.



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Eric Dumazet - July 2, 2012, 9:07 a.m.
On Mon, 2012-07-02 at 11:18 +0800, roy.qing.li@gmail.com wrote:
> From: RongQing.Li <roy.qing.li@gmail.com>
> 
> opt always equals np->opts, so it is meaningless to define opt, and
> check if opt does not equal np->opts and then try to free opt.
> 
> Signed-off-by: RongQing.Li <roy.qing.li@gmail.com>
> ---
>  net/ipv6/tcp_ipv6.c |   16 +++-------------
>  1 files changed, 3 insertions(+), 13 deletions(-)

Acked-by: Eric Dumazet <edumazet@google.com>



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David Miller - July 5, 2012, 10:13 a.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 02 Jul 2012 11:07:47 +0200

> On Mon, 2012-07-02 at 11:18 +0800, roy.qing.li@gmail.com wrote:
>> From: RongQing.Li <roy.qing.li@gmail.com>
>> 
>> opt always equals np->opts, so it is meaningless to define opt, and
>> check if opt does not equal np->opts and then try to free opt.
>> 
>> Signed-off-by: RongQing.Li <roy.qing.li@gmail.com>
>> ---
>>  net/ipv6/tcp_ipv6.c |   16 +++-------------
>>  1 files changed, 3 insertions(+), 13 deletions(-)
> 
> Acked-by: Eric Dumazet <edumazet@google.com>

Ok I now understand better why these changes are correct,
applied.
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Patch

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9c06eaf..6cc67ed 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -486,7 +486,6 @@  static int tcp_v6_send_synack(struct sock *sk, struct dst_entry *dst,
 	struct inet6_request_sock *treq = inet6_rsk(req);
 	struct ipv6_pinfo *np = inet6_sk(sk);
 	struct sk_buff * skb;
-	struct ipv6_txoptions *opt = np->opt;
 	int err = -ENOMEM;
 
 	/* First, grab a route. */
@@ -500,13 +499,11 @@  static int tcp_v6_send_synack(struct sock *sk, struct dst_entry *dst,
 
 		fl6->daddr = treq->rmt_addr;
 		skb_set_queue_mapping(skb, queue_mapping);
-		err = ip6_xmit(sk, skb, fl6, opt, np->tclass);
+		err = ip6_xmit(sk, skb, fl6, np->opt, np->tclass);
 		err = net_xmit_eval(err);
 	}
 
 done:
-	if (opt && opt != np->opt)
-		sock_kfree_s(sk, opt, opt->tot_len);
 	return err;
 }
 
@@ -1229,7 +1226,6 @@  static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 	struct inet_sock *newinet;
 	struct tcp_sock *newtp;
 	struct sock *newsk;
-	struct ipv6_txoptions *opt;
 #ifdef CONFIG_TCP_MD5SIG
 	struct tcp_md5sig_key *key;
 #endif
@@ -1290,7 +1286,6 @@  static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 	}
 
 	treq = inet6_rsk(req);
-	opt = np->opt;
 
 	if (sk_acceptq_is_full(sk))
 		goto out_overflow;
@@ -1359,11 +1354,8 @@  static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 	   but we make one more one thing there: reattach optmem
 	   to newsk.
 	 */
-	if (opt) {
-		newnp->opt = ipv6_dup_options(newsk, opt);
-		if (opt != np->opt)
-			sock_kfree_s(sk, opt, opt->tot_len);
-	}
+	if (np->opt)
+		newnp->opt = ipv6_dup_options(newsk, np->opt);
 
 	inet_csk(newsk)->icsk_ext_hdr_len = 0;
 	if (newnp->opt)
@@ -1410,8 +1402,6 @@  static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 out_overflow:
 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
 out_nonewsk:
-	if (opt && opt != np->opt)
-		sock_kfree_s(sk, opt, opt->tot_len);
 	dst_release(dst);
 out:
 	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);