Re: [PATCHv2 net] icmp: fix icmp_ext_echo_iio parsing in icmp_build_probe

[Eric Dumazet <eric.dumazet@gmail.com>]

On 10/13/21 9:24 PM, 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".
> 
> v1->v2:
>   - To make it more clear, call skb_header_pointer() once only for
>     iio->indent's parsing as Jakub Suggested.
> 
> Fixes: d329ea5bd884 ("icmp: add response to RFC 8335 PROBE messages")
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  net/ipv4/icmp.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
> index 8b30cadff708..bccb2132a464 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);

??? How has this been tested ???

If you pass &_iio for last argument, then you _must_ use sizeof(__iio) (or smaller) too for third argument,
or risk stack overflow, in the case page frag bytes need to be copied into _iio

If the remote peer cooks a malicious packet so that ident_len is big like 1200,
then for sure the kernel will crash,
because sizeof(iio->extobj_hdr) + ident_len will be bigger than sizeof(_iio)


> +	if (!iio)
> +		goto send_mal_query;
> +
>  	status = 0;
>  	dev = NULL;
>  	switch (iio->extobj_hdr.class_type) {