ipv6: avoid overflow of offset in ip6_find_1stfragopt (CVE-2017-7542)

debian/changelog

@@ -25,6 +25,7 @@ linux (4.12.3-1~exp1) UNRELEASED; urgency=medium
 
   [ Salvatore Bonaccorso ]
   * dentry name snapshots (CVE-2017-7533)
+  * ipv6: avoid overflow of offset in ip6_find_1stfragopt (CVE-2017-7542)
 
  -- Ben Hutchings <ben@decadent.org.uk>  Tue, 18 Jul 2017 13:26:41 +0100
 

debian/patches/bugfix/all/ipv6-avoid-overflow-of-offset-in-ip6_find_1stfragopt.patch

@@ -0,0 +1,55 @@
+From: Sabrina Dubroca <sd@queasysnail.net>
+Date: Wed, 19 Jul 2017 22:28:55 +0200
+Subject: ipv6: avoid overflow of offset in ip6_find_1stfragopt
+Origin: https://git.kernel.org/linus/6399f1fae4ec29fab5ec76070435555e256ca3a6
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-7542
+
+In some cases, offset can overflow and can cause an infinite loop in
+ip6_find_1stfragopt(). Make it unsigned int to prevent the overflow, and
+cap it at IPV6_MAXPLEN, since packets larger than that should be invalid.
+
+This problem has been here since before the beginning of git history.
+
+Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
+Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ net/ipv6/output_core.c | 8 ++++++--
+ 1 file changed, 6 insertions(+), 2 deletions(-)
+
+diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
+index e9065b8d3af8..abb2c307fbe8 100644
+--- a/net/ipv6/output_core.c
++++ b/net/ipv6/output_core.c
+@@ -78,7 +78,7 @@ EXPORT_SYMBOL(ipv6_select_ident);
+ 
+ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
+ {
+-	u16 offset = sizeof(struct ipv6hdr);
++	unsigned int offset = sizeof(struct ipv6hdr);
+ 	unsigned int packet_len = skb_tail_pointer(skb) -
+ 		skb_network_header(skb);
+ 	int found_rhdr = 0;
+@@ -86,6 +86,7 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
+ 
+ 	while (offset <= packet_len) {
+ 		struct ipv6_opt_hdr *exthdr;
++		unsigned int len;
+ 
+ 		switch (**nexthdr) {
+ 
+@@ -111,7 +112,10 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
+ 
+ 		exthdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) +
+ 						 offset);
+-		offset += ipv6_optlen(exthdr);
++		len = ipv6_optlen(exthdr);
++		if (len + offset >= IPV6_MAXPLEN)
++			return -EINVAL;
++		offset += len;
+ 		*nexthdr = &exthdr->nexthdr;
+ 	}
+ 
+-- 
+2.11.0
+

debian/patches/series

@@ -118,6 +118,7 @@ features/all/lockdown/arm64-add-kernel-config-option-to-lock-down-when.patch
 # Security fixes
 debian/i386-686-pae-pci-set-pci-nobios-by-default.patch
 bugfix/all/dentry-name-snapshots.patch
+bugfix/all/ipv6-avoid-overflow-of-offset-in-ip6_find_1stfragopt.patch
 
 # Fix exported symbol versions
 bugfix/alpha/alpha-restore-symbol-versions-for-symbols-exported-f.patch