--- /dev/null
+From 75559c167bddc1254db5bcff032ad5eed8bd6f4a Mon Sep 17 00:00:00 2001
+From: Jean Delvare <jdelvare@suse.de>
+Date: Wed, 4 Apr 2007 23:52:46 -0700
+Subject: APPLETALK: Fix a remotely triggerable crash
+
+When we receive an AppleTalk frame shorter than what its header says,
+we still attempt to verify its checksum, and trip on the BUG_ON() at
+the end of function atalk_sum_skb() because of the length mismatch.
+
+This has security implications because this can be triggered by simply
+sending a specially crafted ethernet frame to a target victim,
+effectively crashing that host. Thus this qualifies, I think, as a
+remote DoS. Here is the frame I used to trigger the crash, in npg
+format:
+
+<Appletalk Killer>
+{
+# Ethernet header -----
+
+ XX XX XX XX XX XX # Destination MAC
+ 00 00 00 00 00 00 # Source MAC
+ 00 1D # Length
+
+# LLC header -----
+
+ AA AA 03
+ 08 00 07 80 9B # Appletalk
+
+# Appletalk header -----
+
+ 00 1B # Packet length (invalid)
+ 00 01 # Fake checksum
+ 00 00 00 00 # Destination and source networks
+ 00 00 00 00 # Destination and source nodes and ports
+
+# Payload -----
+
+ 0C 0D 0E 0F 10 11 12 13
+ 14
+}
+
+The destination MAC address must be set to those of the victim.
+
+The severity is mitigated by two requirements:
+* The target host must have the appletalk kernel module loaded. I
+ suspect this isn't so frequent.
+* AppleTalk frames are non-IP, thus I guess they can only travel on
+ local networks. I am no network expert though, maybe it is possible
+ to somehow encapsulate AppleTalk packets over IP.
+
+The bug has been reported back in June 2004:
+ http://bugzilla.kernel.org/show_bug.cgi?id=2979
+But it wasn't investigated, and was closed in July 2006 as both
+reporters had vanished meanwhile.
+
+This code was new in kernel 2.6.0-test5:
+ http://git.kernel.org/?p=linux/kernel/git/tglx/history.git;a=commitdiff;h=7ab442d7e0a76402c12553ee256f756097cae2d2
+And not modified since then, so we can assume that vanilla kernels
+2.6.0-test5 and later, and distribution kernels based thereon, are
+affected.
+
+Note that I still do not know for sure what triggered the bug in the
+real-world cases. The frame could have been corrupted by the kernel if
+we have a bug hiding somewhere. But more likely, we are receiving the
+faulty frame from the network.
+
+Signed-off-by: Jean Delvare <jdelvare@suse.de>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Chris Wright <chrisw@sous-sol.org>
+---
+ net/appletalk/ddp.c | 7 +++++--
+ 1 file changed, 5 insertions(+), 2 deletions(-)
+
+--- linux-2.6.20.4.orig/net/appletalk/ddp.c
++++ linux-2.6.20.4/net/appletalk/ddp.c
+@@ -1417,10 +1417,13 @@ static int atalk_rcv(struct sk_buff *skb
+ /*
+ * Size check to see if ddp->deh_len was crap
+ * (Otherwise we'll detonate most spectacularly
+- * in the middle of recvmsg()).
++ * in the middle of atalk_checksum() or recvmsg()).
+ */
+- if (skb->len < sizeof(*ddp))
++ if (skb->len < sizeof(*ddp) || skb->len < (len_hops & 1023)) {
++ pr_debug("AppleTalk: dropping corrupted frame (deh_len=%u, "
++ "skb->len=%u)\n", len_hops & 1023, skb->len);
+ goto freeit;
++ }
+
+ /*
+ * Any checksums. Note we don't do htons() on this == is assumed to be
projects / thirdparty / kernel / stable-queue.git / commitdiff
