Re: Regression, bisected: reference leak with IPSec since ~2.6.31

[Eric Dumazet]

Le lundi 20 septembre 2010 Ã 22:17 +0200, Eric Dumazet a Ãcrit :
> Le lundi 20 septembre 2010 Ã 15:52 -0400, Nick Bowler a Ãcrit :
> > On 2010-09-20 20:20 +0200, Eric Dumazet wrote:
> > > If you change your program to send small frames (so they are not
> > > fragmented), is the problem still present ?
> > 
> > I changed MAX_DGRAM_SIZE in the test program to 1000 (mtu on the
> > interface is 1500).  The short answer is that the references are
> > not leaked, and things seem to get cleaned up.  So the rest of this
> > mail probably describes a separate issue.
> > 
> > The long answer, however, is interesting: With latest Linus' git, the
> > references are cleaned up much later than I would expect.  After running
> > the test program and flushing the SAD/SPD, the reference count is still
> > 1.  If I repeat the test immediately, the reference count will increase
> > further.  I can easily raise the reference count to, say, 100.  Now, if
> > I wait a while (10 minutes or so), the reference count will still be
> > 100.  However, when I run the setkey script after this delay, the
> > reference count drops immediately to 1.  If I then flush the SAD/SPD, it
> > drops to 0.
> > 
> > This behaviour is new: newer than the reported leak.  For example, with
> > 2.6.34, everything works perfectly with MAX_DGRAM_SIZE set to 1000 (the
> > SAs are destroyed immediately when the SAD/SPD are flushed), but the
> > leak occurs with MAX_DGRAM_SIZE set to 10000.
> > 
> 
> Thanks Nick
> 
> I suspect a skb->truesize bug somewhere.
> 
> I can see atomic_read(&sk->sk_wmem_alloc) becoming negative after a
> while...
> 
> I am investigating and let you know.
> 
> Thanks
> 

OK, I found a bug in ip_fragment() and ip6_fragment()

In case slow_path is hit, we have a truesize mismatch

Could you try following patch ?

Thanks !

[PATCH] ip : fix truesize mismatch in ip fragmentation

We should not set frag->destructor to sock_wkfree() until we are sure we
dont hit slow path in ip_fragment(). Or we risk uncharging
frag->truesize twice, and in the end, having negative socket
sk_wmem_alloc counter, or even freeing socket sooner than expected.

Many thanks to Nick Bowler, who provided a very clean bug report and
test programs.

While Nick bisection pointed to commit 2b85a34e911bf483 (net: No more
expensive sock_hold()/sock_put() on each tx), underlying bug is older.

Reported-and-bisected-by: Nick Bowler <nbowler@xxxxxxxxxxxxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
---
 net/ipv4/ip_output.c  |    8 ++++----
 net/ipv6/ip6_output.c |   10 +++++-----
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 04b6989..126d9b3 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -490,7 +490,6 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 	if (skb_has_frags(skb)) {
 		struct sk_buff *frag;
 		int first_len = skb_pagelen(skb);
-		int truesizes = 0;
 
 		if (first_len - hlen > mtu ||
 		    ((first_len - hlen) & 7) ||
@@ -510,11 +509,13 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 				goto slow_path;
 
 			BUG_ON(frag->sk);
-			if (skb->sk) {
+		}
+		if (skb->sk) {
+			skb_walk_frags(skb, frag) {
 				frag->sk = skb->sk;
 				frag->destructor = sock_wfree;
+				skb->truesize -= frag->truesize;
 			}
-			truesizes += frag->truesize;
 		}
 
 		/* Everything is OK. Generate! */
@@ -524,7 +525,6 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 		frag = skb_shinfo(skb)->frag_list;
 		skb_frag_list_init(skb);
 		skb->data_len = first_len - skb_headlen(skb);
-		skb->truesize -= truesizes;
 		skb->len = first_len;
 		iph->tot_len = htons(first_len);
 		iph->frag_off = htons(IP_MF);
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index d40b330..10983ab 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -639,7 +639,6 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 
 	if (skb_has_frags(skb)) {
 		int first_len = skb_pagelen(skb);
-		int truesizes = 0;
 
 		if (first_len - hlen > mtu ||
 		    ((first_len - hlen) & 7) ||
@@ -658,13 +657,15 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 				goto slow_path;
 
 			BUG_ON(frag->sk);
-			if (skb->sk) {
+		}
+		if (skb->sk) {
+			skb_walk_frags(skb, frag) {
 				frag->sk = skb->sk;
 				frag->destructor = sock_wfree;
-				truesizes += frag->truesize;
+				skb->truesize -= frag->truesize;
 			}
 		}
-
+				
 		err = 0;
 		offset = 0;
 		frag = skb_shinfo(skb)->frag_list;
@@ -693,7 +694,6 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 
 		first_len = skb_pagelen(skb);
 		skb->data_len = first_len - skb_headlen(skb);
-		skb->truesize -= truesizes;
 		skb->len = first_len;
 		ipv6_hdr(skb)->payload_len = htons(first_len -
 						   sizeof(struct ipv6hdr));


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