netdev - [PATCH net] net/ipv4: defensive cipso option parsing

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Message-Id: <20180917151149.22231-1-snu@amazon.com>
Date:   Mon, 17 Sep 2018 17:11:49 +0200
From:   Stefan Nuernberger <snu@...zon.com>
To:     netdev@...r.kernel.org
Cc:     aams@...zon.de, yujuan.qi@...iatek.com, paul@...l-moore.com,
        Stefan Nuernberger <snu@...zon.com>, stable@...r.kernel.org
Subject: [PATCH net] net/ipv4: defensive cipso option parsing

commit 40413955ee26 ("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@...zon.com>
Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>
Reviewed-by: Simon Veith <sveith@...zon.de>
Cc: stable@...r.kernel.org
---
 net/ipv4/cipso_ipv4.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 82178cc69c96..f291b57b8474 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -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)
@@ -1522,9 +1522,11 @@ 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:
+			if (!optptr[1] || optptr[1] > optlen)
+				return NULL;
 			return optptr;
 		case IPOPT_END:
 			return NULL;
@@ -1534,6 +1536,10 @@ unsigned char *cipso_v4_optptr(const struct sk_buff *skb)
 		default:
 			taglen = optptr[1];
 		}
+
+		if (!taglen || taglen > optlen)
+			break;
+
 		optlen -= taglen;
 		optptr += taglen;
 	}
-- 
2.19.0