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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Stefan Nuernberger <snu@amazon.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Simon Veith <sveith@amazon.de>,
        Paul Moore <paul@paul-moore.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 3.18 28/90] net/ipv4: defensive cipso option parsing
Date:   Mon, 19 Nov 2018 17:29:10 +0100
Message-Id: <20181119162625.433836842@linuxfoundation.org>
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3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Nuernberger <snu@amazon.com>

commit 076ed3da0c9b2f88d9157dbe7044a45641ae369e upstream.

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/ipv4/cipso_ipv4.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1580,7 +1580,7 @@ static int cipso_v4_parsetag_loc(const s
  *
  * 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)
@@ -1590,10 +1590,8 @@ unsigned char *cipso_v4_optptr(const str
 	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:
@@ -1602,6 +1600,11 @@ unsigned char *cipso_v4_optptr(const str
 		default:
 			taglen = optptr[1];
 		}
+		if (!taglen || taglen > optlen)
+			return NULL;
+		if (optptr[0] == IPOPT_CIPSO)
+			return optptr;
+
 		optlen -= taglen;
 		optptr += taglen;
 	}