[1/1] UBUNTU: SAUCE: Revert "net: increase fragment memory usage limits"

Message ID 1538501393-20323-2-git-send-email-tyhicks@canonical.com
State New
Headers show
Series
  • CVE-2018-5391 - Mitigation for FragmentSmack
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Commit Message

Tyler Hicks Oct. 2, 2018, 5:29 p.m.
This reverts commit c2a936600f78aea00d3312ea4b66a79a4619f9b4. It
made denial of service attacks on the IP fragment handling easier to
carry out.

CVE-2018-5391

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 include/net/ipv6.h     |  4 ++--
 net/ipv4/ip_fragment.c | 22 +++++++---------------
 2 files changed, 9 insertions(+), 17 deletions(-)

Patch

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 8f73be494503..04a865cb4a83 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -373,8 +373,8 @@  static inline bool ipv6_accept_ra(struct inet6_dev *idev)
 	    idev->cnf.accept_ra;
 }
 
-#define IPV6_FRAG_HIGH_THRESH	(4 * 1024*1024)	/* 4194304 */
-#define IPV6_FRAG_LOW_THRESH	(3 * 1024*1024)	/* 3145728 */
+#define IPV6_FRAG_HIGH_THRESH	(256 * 1024)	/* 262144 */
+#define IPV6_FRAG_LOW_THRESH	(192 * 1024)	/* 196608 */
 #define IPV6_FRAG_TIMEOUT	(60 * HZ)	/* 60 seconds */
 
 int __ipv6_addr_type(const struct in6_addr *addr);
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index d14d741fb05e..bd10399eb916 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -788,22 +788,14 @@  static int __net_init ipv4_frags_init_net(struct net *net)
 {
 	int res;
 
-	/* Fragment cache limits.
-	 *
-	 * The fragment memory accounting code, (tries to) account for
-	 * the real memory usage, by measuring both the size of frag
-	 * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
-	 * and the SKB's truesize.
-	 *
-	 * A 64K fragment consumes 129736 bytes (44*2944)+200
-	 * (1500 truesize == 2944, sizeof(struct ipq) == 200)
-	 *
-	 * We will commit 4MB at one time. Should we cross that limit
-	 * we will prune down to 3MB, making room for approx 8 big 64K
-	 * fragments 8x128k.
+	/*
+	 * Fragment cache limits. We will commit 256K at one time. Should we
+	 * cross that limit we will prune down to 192K. This should cope with
+	 * even the most extreme cases without allowing an attacker to
+	 * measurably harm machine performance.
 	 */
-	net->ipv4.frags.high_thresh = 4 * 1024 * 1024;
-	net->ipv4.frags.low_thresh  = 3 * 1024 * 1024;
+	net->ipv4.frags.high_thresh = 256 * 1024;
+	net->ipv4.frags.low_thresh = 192 * 1024;
 	/*
 	 * Important NOTE! Fragment queue must be destroyed before MSL expires.
 	 * RFC791 is wrong proposing to prolongate timer each fragment arrival