[PATCH net] sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit

[PATCH net] sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit

[Xin Long]

Now sctp increases sk_wmem_alloc by 1 when doing set_owner_w for the
skb allocked in sctp_packet_transmit and decreases by 1 when freeing
this skb.

But when this skb goes through networking stack, some subcomponents
might change skb->truesize and add the same amount on sk_wmem_alloc.
However sctp doesn't know the amount to decrease by, it would cause
a leak on sk->sk_wmem_alloc and the sock can never be freed.

Xiumei found this issue when it hit esp_output_head() by using sctp
over ipsec, where skb->truesize is added and so is sk->sk_wmem_alloc.

Since sctp has used sk_wmem_queued to count for writable space since
Commit cd305c74b0f8 ("sctp: use sk_wmem_queued to check for writable
space"), it's ok to fix it by counting sk_wmem_alloc by skb truesize
in sctp_packet_transmit.

Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
Reported-by: Xiumei Mu <xmu@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/output.c | 21 +--------------------
 1 file changed, 1 insertion(+), 20 deletions(-)

diff --git a/net/sctp/output.c b/net/sctp/output.c
index 67939ad..88dfa6a 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -396,25 +396,6 @@ enum sctp_xmit sctp_packet_append_chunk(struct sctp_packet *packet,
 	return retval;
 }
 
-static void sctp_packet_release_owner(struct sk_buff *skb)
-{
-	sk_free(skb->sk);
-}
-
-static void sctp_packet_set_owner_w(struct sk_buff *skb, struct sock *sk)
-{
-	skb_orphan(skb);
-	skb->sk = sk;
-	skb->destructor = sctp_packet_release_owner;
-
-	/*
-	 * The data chunks have already been accounted for in sctp_sendmsg(),
-	 * therefore only reserve a single byte to keep socket around until
-	 * the packet has been transmitted.
-	 */
-	refcount_inc(&sk->sk_wmem_alloc);
-}
-
 static void sctp_packet_gso_append(struct sk_buff *head, struct sk_buff *skb)
 {
 	if (SCTP_OUTPUT_CB(head)->last == head)
@@ -601,7 +582,7 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
 	if (!head)
 		goto out;
 	skb_reserve(head, packet->overhead + MAX_HEADER);
-	sctp_packet_set_owner_w(head, sk);
+	skb_set_owner_w(head, sk);
 
 	/* set sctp header */
 	sh = skb_push(head, sizeof(struct sctphdr));
-- 
2.1.0

Re: [PATCH net] sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit

[David Miller]

From: Xin Long <lucien.xin@gmail.com>
Date: Sun, 18 Nov 2018 15:07:38 +0800

> Now sctp increases sk_wmem_alloc by 1 when doing set_owner_w for the
> skb allocked in sctp_packet_transmit and decreases by 1 when freeing
> this skb.
> 
> But when this skb goes through networking stack, some subcomponents
> might change skb->truesize and add the same amount on sk_wmem_alloc.
> However sctp doesn't know the amount to decrease by, it would cause
> a leak on sk->sk_wmem_alloc and the sock can never be freed.
> 
> Xiumei found this issue when it hit esp_output_head() by using sctp
> over ipsec, where skb->truesize is added and so is sk->sk_wmem_alloc.
> 
> Since sctp has used sk_wmem_queued to count for writable space since
> Commit cd305c74b0f8 ("sctp: use sk_wmem_queued to check for writable
> space"), it's ok to fix it by counting sk_wmem_alloc by skb truesize
> in sctp_packet_transmit.
> 
> Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
> Reported-by: Xiumei Mu <xmu@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable.

Re: [PATCH net] sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit

[Marcelo Ricardo Leitner]

On Mon, Nov 19, 2018 at 12:39:55PM -0800, David Miller wrote:
> From: Xin Long <lucien.xin@gmail.com>
> Date: Sun, 18 Nov 2018 15:07:38 +0800
> 
> > Now sctp increases sk_wmem_alloc by 1 when doing set_owner_w for the
> > skb allocked in sctp_packet_transmit and decreases by 1 when freeing
> > this skb.
> > 
> > But when this skb goes through networking stack, some subcomponents
> > might change skb->truesize and add the same amount on sk_wmem_alloc.
> > However sctp doesn't know the amount to decrease by, it would cause
> > a leak on sk->sk_wmem_alloc and the sock can never be freed.
> > 
> > Xiumei found this issue when it hit esp_output_head() by using sctp
> > over ipsec, where skb->truesize is added and so is sk->sk_wmem_alloc.
> > 
> > Since sctp has used sk_wmem_queued to count for writable space since
> > Commit cd305c74b0f8 ("sctp: use sk_wmem_queued to check for writable
> > space"), it's ok to fix it by counting sk_wmem_alloc by skb truesize
> > in sctp_packet_transmit.
> > 
> > Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
> > Reported-by: Xiumei Mu <xmu@redhat.com>
> > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> 
> Applied and queued up for -stable.

Dave, is there a way that we can check to which versions you queued it
up?

Asking because even though this patch fixes cac2661c53f3 (v4.10) and
the patch probably applies cleanly, it has a dependency on
cd305c74b0f8 (v4.19) and fixing the issue in older kernels either need
a different fix or backport of cd305c74b0f8 too.

Re: [PATCH net] sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit

[David Miller]

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Tue, 20 Nov 2018 22:56:07 -0200

> On Mon, Nov 19, 2018 at 12:39:55PM -0800, David Miller wrote:
>> From: Xin Long <lucien.xin@gmail.com>
>> Date: Sun, 18 Nov 2018 15:07:38 +0800
>> 
>> > Now sctp increases sk_wmem_alloc by 1 when doing set_owner_w for the
>> > skb allocked in sctp_packet_transmit and decreases by 1 when freeing
>> > this skb.
>> > 
>> > But when this skb goes through networking stack, some subcomponents
>> > might change skb->truesize and add the same amount on sk_wmem_alloc.
>> > However sctp doesn't know the amount to decrease by, it would cause
>> > a leak on sk->sk_wmem_alloc and the sock can never be freed.
>> > 
>> > Xiumei found this issue when it hit esp_output_head() by using sctp
>> > over ipsec, where skb->truesize is added and so is sk->sk_wmem_alloc.
>> > 
>> > Since sctp has used sk_wmem_queued to count for writable space since
>> > Commit cd305c74b0f8 ("sctp: use sk_wmem_queued to check for writable
>> > space"), it's ok to fix it by counting sk_wmem_alloc by skb truesize
>> > in sctp_packet_transmit.
>> > 
>> > Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
>> > Reported-by: Xiumei Mu <xmu@redhat.com>
>> > Signed-off-by: Xin Long <lucien.xin@gmail.com>
>> 
>> Applied and queued up for -stable.
> 
> Dave, is there a way that we can check to which versions you queued it
> up?

I queued up the patch is, and then do backports as needed.

If you think it's too complex to backport this, I'll toss it from the
-stable queue and that's what I have just done.