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Date: Wed, 17 Nov 2021 10:44:26 -0800 From: Kees Cook <keescook@...omium.org> To: Jordy Zomer <jordy@...ing.systems> Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, Steffen Klassert <steffen.klassert@...unet.com>, Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org Subject: Re: [PATCH] ipv6: check return value of ipv6_skip_exthdr On Wed, Nov 17, 2021 at 07:16:10PM +0100, Jordy Zomer wrote: > The offset value is used in pointer math on skb->data. > Since ipv6_skip_exthdr may return -1 the pointer to uh and th > may not point to the actual udp and tcp headers and potentially > overwrite other stuff. This is why I think this should be checked. > > Signed-off-by: Jordy Zomer <jordy@...ing.systems> > --- > net/ipv6/esp6.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c > index ed2f061b8768..dc4251655df9 100644 > --- a/net/ipv6/esp6.c > +++ b/net/ipv6/esp6.c > @@ -808,6 +808,11 @@ int esp6_input_done2(struct sk_buff *skb, int err) > struct tcphdr *th; > > offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off); > + > + if (offset < 0) > + err = -EINVAL; > + goto out; > + Ew. Yeah, it seems like ipv6_skip_exthdr() needs to be checked in a lot of places. If this is part of protocol decoding, I'm surprised fuzzers haven't found this? Is this state reachable? I assume so, as there have been similar fixes in the past: https://git.kernel.org/linus/92c6058024e87087cf1b99b0389d67c0a886360e > uh = (void *)(skb->data + offset); > th = (void *)(skb->data + offset); > hdr_len += offset; > -- > 2.27.0 > -- Kees Cook
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