Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=75559c167bddc1254db5bcff032ad5eed8bd6f4a
Commit: 75559c167bddc1254db5bcff032ad5eed8bd6f4a
Parent: 58e949139014a852a83b5ef071136b1f50c86ad1
Author: Jean Delvare <[EMAIL PROTECTED]>
AuthorDate: Wed Apr 4 23:52:46 2007 -0700
Committer: David S. Miller <[EMAIL PROTECTED]>
CommitDate: Wed Apr 4 23:52:46 2007 -0700
[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 <[EMAIL PROTECTED]>
Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
---
net/appletalk/ddp.c | 7 +++++--
1 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 113c175..c8b7dc2 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1417,10 +1417,13 @@ static int atalk_rcv(struct sk_buff *skb, struct
net_device *dev,
/*
* 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
-
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