Re: Is this a bug in linux-2.6.12 ipsec code function xfrm4_rcv_encap ??

[k8 s <uint32@gmail.com>]

I AM SORRY FOR THE PREVIOUS MAIL.
I am correcting my previous mail. 
Infact I see only One race(not three as was wrongly pointed out).
I commented out the section once again where the race might be.


On 7/23/05, k8 s <uint32@gmail.com> wrote:
> Hello,
> I see a possible race in linux-2.6.12 ipsec code function xfrm4_rcv_encap.
> I want to double check with the group.
> The issue is with SMP(mostly) or Preemptible Kernels.
> The race comes when someone flushes the SA's
> (setkey -Fexecuting  on another processor )
> while xfrm_rcv_encap is executing one processor.
> 
> Below is the function code.
> I am putting comments in the code where probably the race comes.
> correct me if I am wrong.
> 
> int xfrm4_rcv_encap(struct sk_buff *skb, __u16 encap_type)
> {
>         int err;
>         u32 spi, seq;
>         struct sec_decap_state xfrm_vec[XFRM_MAX_DEPTH];
>         struct xfrm_state *x;
>         int xfrm_nr = 0;
>         int decaps = 0;
> 
>         if ((err = xfrm4_parse_spi(skb, skb->nh.iph->protocol, &spi, &seq)) != 0)
>                 goto drop;
> 
>         do {
>                 struct iphdr *iph = skb->nh.iph;
> 
>                 if (xfrm_nr == XFRM_MAX_DEPTH)
>                         goto drop;
> 
>                 x = xfrm_state_lookup((xfrm_address_t *)&iph->daddr, spi,
> iph->protocol, AF_INET);
> 

>                 if (x == NULL)
>                         goto drop;
> 
>                 spin_lock(&x->lock);
>                 if (unlikely(x->km.state != XFRM_STATE_VALID))
>                         goto drop_unlock;
> 
>                 if (x->props.replay_window && xfrm_replay_check(x, seq))
>                         goto drop_unlock;
> 
>                 if (xfrm_state_check_expire(x))
>                         goto drop_unlock;
> 
>                 xfrm_vec[xfrm_nr].decap.decap_type = encap_type;
>                 if (x->type->input(x, &(xfrm_vec[xfrm_nr].decap), skb))
>                         goto drop_unlock;
> 
>                 /* only the first xfrm gets the encap type */
>                 encap_type = 0;
> 
>                 if (x->props.replay_window)
>                         xfrm_replay_advance(x, seq);
> 
>                 x->curlft.bytes += skb->len;
>                 x->curlft.packets++;
> 
>                 spin_unlock(&x->lock);
> 
>                 xfrm_vec[xfrm_nr++].xvec = x;
> 
>                 iph = skb->nh.iph;
> 
 /********************************************************
 Race Here . The Check(x->props.mode) is without Lock. What if setkey
-F is done at the same time on another processor freeing what x points
to.
 ********************************************************/
>                 if (x->props.mode) {
>                         if (iph->protocol != IPPROTO_IPIP)
>                                 goto drop;
>                         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
>                                 goto drop;
>                         if (skb_cloned(skb) &&
>                             pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
>                                 goto drop;
>                         if (x->props.flags & XFRM_STATE_DECAP_DSCP)
>                                 ipv4_copy_dscp(iph, skb->h.ipiph);
>                         if (!(x->props.flags & XFRM_STATE_NOECN))
>                                 ipip_ecn_decapsulate(skb);
>                         skb->mac.raw = memmove(skb->data - skb->mac_len,
>                                                skb->mac.raw, skb->mac_len);
>                         skb->nh.raw = skb->data;
>                         memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
>                         decaps = 1;
>                         break;
>                 }
> 
>                 if ((err = xfrm_parse_spi(skb, skb->nh.iph->protocol, &spi, &seq)) < 0)
>                         goto drop;
>         } while (!err);
> 
>         /* Allocate new secpath or COW existing one. */
> 
>         if (!skb->sp || atomic_read(&skb->sp->refcnt) != 1) {
>                 struct sec_path *sp;
>                 sp = secpath_dup(skb->sp);
>                 if (!sp)
>                         goto drop;
>                 if (skb->sp)
>                         secpath_put(skb->sp);
>                 skb->sp = sp;
>         }
>         if (xfrm_nr + skb->sp->len > XFRM_MAX_DEPTH)
>                 goto drop;
> 
>         memcpy(skb->sp->x+skb->sp->len, xfrm_vec, xfrm_nr*sizeof(struct
> sec_decap_state));
>         skb->sp->len += xfrm_nr;
> 
>         if (decaps) {
>                 if (!(skb->dev->flags&IFF_LOOPBACK)) {
>                         dst_release(skb->dst);
>                         skb->dst = NULL;
>                 }
>                 netif_rx(skb);
>                 return 0;
>         } else {
>                 return -skb->nh.iph->protocol;
>         }
> 
> drop_unlock:
>         spin_unlock(&x->lock);
>         xfrm_state_put(x);
> drop:
>         while (--xfrm_nr >= 0)
>                 xfrm_state_put(xfrm_vec[xfrm_nr].xvec);
> 
>         kfree_skb(skb);
>         return 0;
> }
> 
> 
> 
> 
> 
> I am just guessing.
> If I am wrong I request anyone to give me a reason why it is not a bug ?
> I haven't checked the IPv6 front and the IPSec outbound side.
> Once this proves to be a bug I will check them.
> 
> S.Kartikeyan
>
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