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net/ipv4: defensive cipso option parsing 

commit 40413955ee ("Cipso: cipso_v4_optptr enter infinite loop") fixed
a possible infinite loop in the IP option parsing of CIPSO. The fix
assumes that ip_options_compile filtered out all zero length options and
that no other one-byte options beside IPOPT_END and IPOPT_NOOP exist.
While this assumption currently holds true, add explicit checks for zero
length and invalid length options to be safe for the future. Even though
ip_options_compile should have validated the options, the introduction of
new one-byte options can still confuse this code without the additional
checks.

Signed-off-by: Stefan Nuernberger <snu@amazon.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Simon Veith <sveith@amazon.de>
Cc: stable@vger.kernel.org
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Stefan Nuernberger 2018-09-17 19:46:53 +02:00 committed by David S. Miller
parent 0020f5c807
commit 076ed3da0c
1 changed files with 7 additions and 4 deletions
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11
net/ipv4/cipso_ipv4.c
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@ -1512,7 +1512,7 @@ static int cipso_v4_parsetag_loc(const struct cipso_v4_doi *doi_def,
*
* Description:
* Parse the packet's IP header looking for a CIPSO option. Returns a pointer
* to the start of the CIPSO option on success, NULL if one if not found.
* to the start of the CIPSO option on success, NULL if one is not found.
*
*/
unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
@ -1522,10 +1522,8 @@ unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
int optlen;
int taglen;
for (optlen = iph->ihl*4 - sizeof(struct iphdr); optlen > 0; ) {
for (optlen = iph->ihl*4 - sizeof(struct iphdr); optlen > 1; ) {
switch (optptr[0]) {
case IPOPT_CIPSO:
return optptr;
case IPOPT_END:
return NULL;
case IPOPT_NOOP:
@ -1534,6 +1532,11 @@ unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
default:
taglen = optptr[1];
}
if (!taglen || taglen > optlen)
return NULL;
if (optptr[0] == IPOPT_CIPSO)
return optptr;
optlen -= taglen;
optptr += taglen;
}