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ipv6: protect mtu calculation of wrap-around and infinite loop by rounding issues 

Raw sockets with hdrincl enabled can insert ipv6 extension headers
right into the data stream. In case we need to fragment those packets,
we reparse the options header to find the place where we can insert
the fragment header. If the extension headers exceed the link's MTU we
actually cannot make progress in such a case.

Instead of ending up in broken arithmetic or rounding towards 0 and
entering an endless loop in ip6_fragment, just prevent those cases by
aborting early and signal -EMSGSIZE to user space.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hannes Frederic Sowa 2015-10-16 11:32:43 +02:00 committed by David S. Miller
parent 79907146fb
commit b72a2b01b6
1 changed files with 5 additions and 1 deletions
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6
net/ipv6/ip6_output.c
View File

@ -28,6 +28,7 @@
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/overflow-arith.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/net.h>
@ -584,7 +585,10 @@ int ip6_fragment(struct sock *sk, struct sk_buff *skb,
if (np->frag_size)
mtu = np->frag_size;
}
mtu -= hlen + sizeof(struct frag_hdr);
if (overflow_usub(mtu, hlen + sizeof(struct frag_hdr), &mtu) ||
mtu <= 7)
goto fail_toobig;
frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
&ipv6_hdr(skb)->saddr);