Commit 89bc7848 authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by David S. Miller
Browse files

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.

This is the second version of the patch which doesn't use the
overflow_usub function, which got reverted for now.

Suggested-by: default avatarLinus Torvalds <>
Cc: Linus Torvalds <>
Reported-by: default avatarDmitry Vyukov <>
Cc: Dmitry Vyukov <>
Signed-off-by: default avatarHannes Frederic Sowa <>
Signed-off-by: default avatarDavid S. Miller <>
parent 1e0d69a9
......@@ -584,6 +584,8 @@ int ip6_fragment(struct sock *sk, struct sk_buff *skb,
if (np->frag_size)
mtu = np->frag_size;
if (mtu < hlen + sizeof(struct frag_hdr) + 8)
goto fail_toobig;
mtu -= hlen + sizeof(struct frag_hdr);
frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
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