| Message ID | 1355132466.9857.6.camel@jlt4.sipsolutions.net |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
Hello, On Mon, 2012-12-10 at 10:41 +0100, Johannes Berg wrote: > From: Johannes Berg <johannes.berg@intel.com> > > ip_check_defrag() might be called from af_packet within the > RX path where shared SKBs are used, so it must not modify > the input SKB before it has unshared it for defragmentation. > Use skb_copy_bits() to get the IP header and only pull in > everything later. > > The same is true for the other caller in macvlan as it is > called from dev->rx_handler which can also get a shared SKB. I've applied the patch and built a new kernel. I did not manage to get it crashed when using the two techniques (suspend to ram and down/up interface) that were working well to crash kernel without the patch. BR, > Reported-by: Eric Leblond <eric@regit.org> > Cc: stable@vger.kernel.org > Signed-off-by: Johannes Berg <johannes.berg@intel.com> > --- > For some versions of the kernel, this code goes into af_packet.c > > net/ipv4/ip_fragment.c | 19 +++++++++---------- > 1 file changed, 9 insertions(+), 10 deletions(-) > > diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c > index 448e685..8d5cc75 100644 > --- a/net/ipv4/ip_fragment.c > +++ b/net/ipv4/ip_fragment.c > @@ -707,28 +707,27 @@ EXPORT_SYMBOL(ip_defrag); > > struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user) > { > - const struct iphdr *iph; > + struct iphdr iph; > u32 len; > > if (skb->protocol != htons(ETH_P_IP)) > return skb; > > - if (!pskb_may_pull(skb, sizeof(struct iphdr))) > + if (!skb_copy_bits(skb, 0, &iph, sizeof(iph))) > return skb; > > - iph = ip_hdr(skb); > - if (iph->ihl < 5 || iph->version != 4) > + if (iph.ihl < 5 || iph.version != 4) > return skb; > - if (!pskb_may_pull(skb, iph->ihl*4)) > - return skb; > - iph = ip_hdr(skb); > - len = ntohs(iph->tot_len); > - if (skb->len < len || len < (iph->ihl * 4)) > + > + len = ntohs(iph.tot_len); > + if (skb->len < len || len < (iph.ihl * 4)) > return skb; > > - if (ip_is_fragment(ip_hdr(skb))) { > + if (ip_is_fragment(&iph)) { > skb = skb_share_check(skb, GFP_ATOMIC); > if (skb) { > + if (!pskb_may_pull(skb, iph.ihl*4)) > + return skb; > if (pskb_trim_rcsum(skb, len)) > return skb; > memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
From: Johannes Berg <johannes@sipsolutions.net> Date: Mon, 10 Dec 2012 10:41:06 +0100 > From: Johannes Berg <johannes.berg@intel.com> > > ip_check_defrag() might be called from af_packet within the > RX path where shared SKBs are used, so it must not modify > the input SKB before it has unshared it for defragmentation. > Use skb_copy_bits() to get the IP header and only pull in > everything later. > > The same is true for the other caller in macvlan as it is > called from dev->rx_handler which can also get a shared SKB. > > Reported-by: Eric Leblond <eric@regit.org> > Cc: stable@vger.kernel.org > Signed-off-by: Johannes Berg <johannes.berg@intel.com> > --- > For some versions of the kernel, this code goes into af_packet.c So the bug is that ip_check_defrag() has a precondition which is met properly by all callers except AF_PACKET. If this is the case, remind me why are we changing ip_check_defrag() rather than the violator of the precondition? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, 2012-12-10 at 13:41 -0500, David Miller wrote: > From: Johannes Berg <johannes@sipsolutions.net> > Date: Mon, 10 Dec 2012 10:41:06 +0100 > > > From: Johannes Berg <johannes.berg@intel.com> > > > > ip_check_defrag() might be called from af_packet within the > > RX path where shared SKBs are used, so it must not modify > > the input SKB before it has unshared it for defragmentation. > > Use skb_copy_bits() to get the IP header and only pull in > > everything later. > > > > The same is true for the other caller in macvlan as it is > > called from dev->rx_handler which can also get a shared SKB. > > > > Reported-by: Eric Leblond <eric@regit.org> > > Cc: stable@vger.kernel.org > > Signed-off-by: Johannes Berg <johannes.berg@intel.com> > > --- > > For some versions of the kernel, this code goes into af_packet.c > > So the bug is that ip_check_defrag() has a precondition which is met > properly by all callers except AF_PACKET. > > If this is the case, remind me why are we changing ip_check_defrag() > rather than the violator of the precondition? I don't think this is the case. If you're referring to my note about af_packet: the kernels where this goes into af_packet.c are the kernels that don't even have ip_check_defrag() because macvlan didn't exist/didn't have ip defrag support and af_packet had this code there -- see commit bc416d9768a. If you're not referring to my note about af_packet: both callers (there are only two) of ip_check_defrag() have this bug as far as I can tell because they're both in the part of the RX path where shared SKBs might happen. johannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Johannes Berg <johannes@sipsolutions.net> Date: Mon, 10 Dec 2012 19:45:52 +0100 > On Mon, 2012-12-10 at 13:41 -0500, David Miller wrote: >> So the bug is that ip_check_defrag() has a precondition which is met >> properly by all callers except AF_PACKET. >> >> If this is the case, remind me why are we changing ip_check_defrag() >> rather than the violator of the precondition? > > I don't think this is the case. > > If you're referring to my note about af_packet: the kernels where this > goes into af_packet.c are the kernels that don't even have > ip_check_defrag() because macvlan didn't exist/didn't have ip defrag > support and af_packet had this code there -- see commit bc416d9768a. > > If you're not referring to my note about af_packet: both callers (there > are only two) of ip_check_defrag() have this bug as far as I can tell > because they're both in the part of the RX path where shared SKBs might > happen. You're right, I misinterpreted what's happening here. My misunderstanding was that this was a situation where normal IPV4 input processing makes sure the SKB is unshared, and we had special code paths that didn't make sure that was the case. Rather, here, we have a special entrypoint for macvlan and AF_PACKET which is supposed to take care of such issues since it is known to execute in a different kind of environment. I'm pretty sure I'll apply this, after I check a few more things, thanks Johannes! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index 448e685..8d5cc75 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -707,28 +707,27 @@ EXPORT_SYMBOL(ip_defrag); struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user) { - const struct iphdr *iph; + struct iphdr iph; u32 len; if (skb->protocol != htons(ETH_P_IP)) return skb; - if (!pskb_may_pull(skb, sizeof(struct iphdr))) + if (!skb_copy_bits(skb, 0, &iph, sizeof(iph))) return skb; - iph = ip_hdr(skb); - if (iph->ihl < 5 || iph->version != 4) + if (iph.ihl < 5 || iph.version != 4) return skb; - if (!pskb_may_pull(skb, iph->ihl*4)) - return skb; - iph = ip_hdr(skb); - len = ntohs(iph->tot_len); - if (skb->len < len || len < (iph->ihl * 4)) + + len = ntohs(iph.tot_len); + if (skb->len < len || len < (iph.ihl * 4)) return skb; - if (ip_is_fragment(ip_hdr(skb))) { + if (ip_is_fragment(&iph)) { skb = skb_share_check(skb, GFP_ATOMIC); if (skb) { + if (!pskb_may_pull(skb, iph.ihl*4)) + return skb; if (pskb_trim_rcsum(skb, len)) return skb; memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));