On Sat, Oct 06, 2012 at 05:38:04PM +0200, Krzysztof Mazur wrote:
> On Sat, Oct 06, 2012 at 02:32:50PM +0100, David Woodhouse wrote:
> > On Sat, 2012-10-06 at 14:19 +0200, Krzysztof Mazur wrote:
> > > Now pppoatm_send(), like vcc_sendmsg(), checks for vcc flags that
> > > indicate that vcc is not ready.
> >
> > And what locking prevents the flag from being set immediately after we
> > check it?
> >
>
> nothing, this patch should fix this.
>
>
> vcc = ATM_SKB(skb)->vcc;
> + bh_lock_sock(sk_atm(vcc));
After bh_lock_sock() sock_owned_by_user(sk_atm(vcc)) should be checked
here. I'm sending fixed patch.
> if (test_bit(ATM_VF_RELEASED, &vcc->flags)
> || test_bit(ATM_VF_CLOSE, &vcc->flags)
Krzysiek
--
>From 3ae93335423ed0ba526dc80163ff6dfeba9bbea1 Mon Sep 17 00:00:00 2001
From: Krzysztof Mazur <krzys...@podlesie.net>
Date: Mon, 8 Oct 2012 08:10:22 +0200
Subject: [PATCH] pppoatm: fix race condition with destroying of vcc
The pppoatm_send() calls vcc->send() and now also checks for
some vcc flags that indicate destroyed vcc without proper locking.
The vcc_sendmsg() uses lock_sock(sk). This lock is used by
vcc_release(), so vcc_destroy_socket() will not be called between
check and during ->send(). The vcc_release_async() sets ATM_VF_CLOSE,
but it should be safe to call ->send() after it, because
vcc->dev->ops->close() is not called.
The pppoatm_send() is called with BH disabled, so bh_lock_sock()
should be used instead of lock_sock().
Signed-off-by: Krzysztof Mazur <krzys...@podlesie.net>
---
net/atm/pppoatm.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
index 0dcb5dc..e3b2d69 100644
--- a/net/atm/pppoatm.c
+++ b/net/atm/pppoatm.c
@@ -270,6 +270,7 @@ static int pppoatm_send(struct ppp_channel *chan, struct
sk_buff *skb)
{
struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
struct atm_vcc *vcc;
+ int ret;
ATM_SKB(skb)->vcc = pvcc->atmvcc;
pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
@@ -304,17 +305,24 @@ static int pppoatm_send(struct ppp_channel *chan, struct
sk_buff *skb)
}
vcc = ATM_SKB(skb)->vcc;
+ bh_lock_sock(sk_atm(vcc));
+ if (sock_owned_by_user(sk_atm(vcc)))
+ goto nospace_unlock_sock;
if (test_bit(ATM_VF_RELEASED, &vcc->flags)
|| test_bit(ATM_VF_CLOSE, &vcc->flags)
|| !test_bit(ATM_VF_READY, &vcc->flags))
- goto nospace;
+ goto nospace_unlock_sock;
atomic_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
- return ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
+ ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
? DROP_PACKET : 1;
+ bh_unlock_sock(sk_atm(vcc));
+ return ret;
+nospace_unlock_sock:
+ bh_unlock_sock(sk_atm(vcc));
nospace:
/*
* We don't have space to send this SKB now, but we might have
--
1.7.12.2.2.g1c3c581
--
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