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Date: Thu, 14 Oct 2021 11:59:40 +0800
From: Xin Long <lucien.xin@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
Dan Carpenter <dan.carpenter@...cle.com>,
Andreas Roeseler <andreas.a.roeseler@...il.com>
Subject: Re: [PATCH net] icmp: fix icmp_ext_echo_iio parsing in icmp_build_probe
On Thu, Oct 14, 2021 at 11:39 AM Xin Long <lucien.xin@...il.com> wrote:
>
> On Thu, Oct 14, 2021 at 12:31 AM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Tue, 12 Oct 2021 04:43:07 -0400 Xin Long wrote:
> > > In icmp_build_probe(), the icmp_ext_echo_iio parsing should be done
> > > step by step and skb_header_pointer() return value should always be
> > > checked, this patch fixes 3 places in there:
> > >
> > > - On case ICMP_EXT_ECHO_CTYPE_NAME, it should only copy ident.name
> > > from skb by skb_header_pointer(), its len is ident_len. Besides,
> > > the return value of skb_header_pointer() should always be checked.
> > >
> > > - On case ICMP_EXT_ECHO_CTYPE_INDEX, move ident_len check ahead of
> > > skb_header_pointer(), and also do the return value check for
> > > skb_header_pointer().
> > >
> > > - On case ICMP_EXT_ECHO_CTYPE_ADDR, before accessing iio->ident.addr.
> > > ctype3_hdr.addrlen, skb_header_pointer() should be called first,
> > > then check its return value and ident_len.
> > > On subcases ICMP_AFI_IP and ICMP_AFI_IP6, also do check for ident.
> > > addr.ctype3_hdr.addrlen and skb_header_pointer()'s return value.
> > > On subcase ICMP_AFI_IP, the len for skb_header_pointer() should be
> > > "sizeof(iio->extobj_hdr) + sizeof(iio->ident.addr.ctype3_hdr) +
> > > sizeof(struct in_addr)" or "ident_len".
> > >
> > > Fixes: d329ea5bd884 ("icmp: add response to RFC 8335 PROBE messages")
> > > Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> > > Signed-off-by: Xin Long <lucien.xin@...il.com>
> >
> > > diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> > > index 8b30cadff708..818c79266c48 100644
> > > --- a/net/ipv4/icmp.c
> > > +++ b/net/ipv4/icmp.c
> > > @@ -1061,38 +1061,48 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
> > > dev = NULL;
> > > switch (iio->extobj_hdr.class_type) {
> > > case ICMP_EXT_ECHO_CTYPE_NAME:
> > > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
> > > if (ident_len >= IFNAMSIZ)
> > > goto send_mal_query;
> > > + iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > > + ident_len, &_iio);
> > > + if (!iio)
> > > + goto send_mal_query;
> > > memset(buff, 0, sizeof(buff));
> > > memcpy(buff, &iio->ident.name, ident_len);
> > > dev = dev_get_by_name(net, buff);
> > > break;
> > > case ICMP_EXT_ECHO_CTYPE_INDEX:
> > > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > > - sizeof(iio->ident.ifindex), &_iio);
> > > if (ident_len != sizeof(iio->ident.ifindex))
> > > goto send_mal_query;
> > > + iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > > + ident_len, &_iio);
> > > + if (!iio)
> > > + goto send_mal_query;
> > > dev = dev_get_by_index(net, ntohl(iio->ident.ifindex));
> > > break;
> > > case ICMP_EXT_ECHO_CTYPE_ADDR:
> > > - if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
> > > - iio->ident.addr.ctype3_hdr.addrlen)
> > > + iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > > + sizeof(iio->ident.addr.ctype3_hdr), &_iio);
> > > + if (!iio || ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
> > > + iio->ident.addr.ctype3_hdr.addrlen)
> > > goto send_mal_query;
> > > switch (ntohs(iio->ident.addr.ctype3_hdr.afi)) {
> > > case ICMP_AFI_IP:
> > > + if (iio->ident.addr.ctype3_hdr.addrlen != sizeof(struct in_addr))
> > > + goto send_mal_query;
> > > iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > > - sizeof(struct in_addr), &_iio);
> > > - if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
> > > - sizeof(struct in_addr))
> > > + ident_len, &_iio);
> > > + if (!iio)
> > > goto send_mal_query;
> > > dev = ip_dev_find(net, iio->ident.addr.ip_addr.ipv4_addr);
> > > break;
> > > #if IS_ENABLED(CONFIG_IPV6)
> > > case ICMP_AFI_IP6:
> > > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
> > > - if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
> > > - sizeof(struct in6_addr))
> > > + if (iio->ident.addr.ctype3_hdr.addrlen != sizeof(struct in6_addr))
> > > + goto send_mal_query;
> > > + iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > > + ident_len, &_iio);
> > > + if (!iio)
> > > goto send_mal_query;
> > > dev = ipv6_stub->ipv6_dev_find(net, &iio->ident.addr.ip_addr.ipv6_addr, dev);
> > > dev_hold(dev);
> >
> > If I'm reading this right we end up with the same skb_header_pointer
> > call 4 times, every path ends up calling:
> >
> > skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) + ident_len, &_iio);
> >
> > and looks like the skb does not get modified in between so these calls
> > are equivalent.
> This looks much clearer.
>
> I was worrying that ident_len might be too big, and ident_len should be verified
> before calling skb_header_pointer(ident_len).
> But it should be okay as skb_header_pointer() will return NULL if ident_len is
> too big.
>
> Will post v2 with the suggestion, thanks!
>
> >
> > So why don't we instead consolidate the paths:
> >
> > diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> > index 8b30cadff708..efa2ec1a85bf 100644
> > --- a/net/ipv4/icmp.c
> > +++ b/net/ipv4/icmp.c
> > @@ -1057,11 +1057,15 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
> > if (ntohs(iio->extobj_hdr.length) <= sizeof(iio->extobj_hdr))
> > goto send_mal_query;
> > ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio->extobj_hdr);
> > + iio = skb_header_pointer(skb, sizeof(_ext_hdr),
> > + sizeof(iio->extobj_hdr) + ident_len, &_iio);
> > + if (!iio)
> > + goto send_mal_query;
> > +
[a]
> > status = 0;
> > dev = NULL;
> > switch (iio->extobj_hdr.class_type) {
> > case ICMP_EXT_ECHO_CTYPE_NAME:
> > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
> > if (ident_len >= IFNAMSIZ)
> > goto send_mal_query;
> > memset(buff, 0, sizeof(buff));
> > @@ -1069,8 +1073,6 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
> > dev = dev_get_by_name(net, buff);
> > break;
> > case ICMP_EXT_ECHO_CTYPE_INDEX:
> > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > - sizeof(iio->ident.ifindex), &_iio);
> > if (ident_len != sizeof(iio->ident.ifindex))
> > goto send_mal_query;
> > dev = dev_get_by_index(net, ntohl(iio->ident.ifindex));
> > @@ -1081,18 +1083,13 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
> > goto send_mal_query;
But, here is another check:
if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
iio->ident.addr.ctype3_hdr.addrlen)
goto send_mal_query;
Thinking if ident_len < sizeof(iio->ident.addr.ctype3_hdr),
iio->ident.addr.ctype3_hdr.addrlen
access could be overflow. So we may do: if (ident_len <
sizeof(iio->ident.addr.ctype3_hdr)) check
before calling skb_header_pointer() in the place [a] above, like:
ident_len = ntohs(iio->extobj_hdr.length) - sizeof(iio->extobj_hdr);
if (ident_len < 4) /* 4 is the minimal size for any class_type */
goto send_mal_query;
iio = skb_header_pointer(skb, sizeof(_ext_hdr),
sizeof(iio->extobj_hdr) + ident_len, &_iio);
if (!iio)
goto send_mal_query;
what do you think?
> > switch (ntohs(iio->ident.addr.ctype3_hdr.afi)) {
> > case ICMP_AFI_IP:
> > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(iio->extobj_hdr) +
> > - sizeof(struct in_addr), &_iio);
> > - if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
> > - sizeof(struct in_addr))
> > + if (iio->ident.addr.ctype3_hdr.addrlen != sizeof(struct in_addr))
> > goto send_mal_query;
> > dev = ip_dev_find(net, iio->ident.addr.ip_addr.ipv4_addr);
> > break;
> > #if IS_ENABLED(CONFIG_IPV6)
> > case ICMP_AFI_IP6:
> > - iio = skb_header_pointer(skb, sizeof(_ext_hdr), sizeof(_iio), &_iio);
> > - if (ident_len != sizeof(iio->ident.addr.ctype3_hdr) +
> > - sizeof(struct in6_addr))
> > + if (iio->ident.addr.ctype3_hdr.addrlen != sizeof(struct in6_addr))
> > goto send_mal_query;
> > dev = ipv6_stub->ipv6_dev_find(net, &iio->ident.addr.ip_addr.ipv6_addr, dev);
> > dev_hold(dev);
> > --
> > 2.31.1
> >
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