Patch "KEYS: Fix ASN.1 indefinite length object parsing" has been added to the 3.18-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KEYS: Fix ASN.1 indefinite length object parsing

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     keys-fix-asn.1-indefinite-length-object-parsing.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 23c8a812dc3c621009e4f0e5342aa4e2ede1ceaa Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Tue, 23 Feb 2016 11:03:12 +0000
Subject: KEYS: Fix ASN.1 indefinite length object parsing

From: David Howells <dhowells@redhat.com>

commit 23c8a812dc3c621009e4f0e5342aa4e2ede1ceaa upstream.

This fixes CVE-2016-0758.

In the ASN.1 decoder, when the length field of an ASN.1 value is extracted,
it isn't validated against the remaining amount of data before being added
to the cursor.  With a sufficiently large size indicated, the check:

	datalen - dp < 2

may then fail due to integer overflow.

Fix this by checking the length indicated against the amount of remaining
data in both places a definite length is determined.

Whilst we're at it, make the following changes:

 (1) Check the maximum size of extended length does not exceed the capacity
     of the variable it's being stored in (len) rather than the type that
     variable is assumed to be (size_t).

 (2) Compare the EOC tag to the symbolic constant ASN1_EOC rather than the
     integer 0.

 (3) To reduce confusion, move the initialisation of len outside of:

	for (len = 0; n > 0; n--) {

     since it doesn't have anything to do with the loop counter n.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 lib/asn1_decoder.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

--- a/lib/asn1_decoder.c
+++ b/lib/asn1_decoder.c
@@ -69,7 +69,7 @@ next_tag:
 
 	/* Extract a tag from the data */
 	tag = data[dp++];
-	if (tag == 0) {
+	if (tag == ASN1_EOC) {
 		/* It appears to be an EOC. */
 		if (data[dp++] != 0)
 			goto invalid_eoc;
@@ -91,10 +91,8 @@ next_tag:
 
 	/* Extract the length */
 	len = data[dp++];
-	if (len <= 0x7f) {
-		dp += len;
-		goto next_tag;
-	}
+	if (len <= 0x7f)
+		goto check_length;
 
 	if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
 		/* Indefinite length */
@@ -105,14 +103,18 @@ next_tag:
 	}
 
 	n = len - 0x80;
-	if (unlikely(n > sizeof(size_t) - 1))
+	if (unlikely(n > sizeof(len) - 1))
 		goto length_too_long;
 	if (unlikely(n > datalen - dp))
 		goto data_overrun_error;
-	for (len = 0; n > 0; n--) {
+	len = 0;
+	for (; n > 0; n--) {
 		len <<= 8;
 		len |= data[dp++];
 	}
+check_length:
+	if (len > datalen - dp)
+		goto data_overrun_error;
 	dp += len;
 	goto next_tag;
 


Patches currently in stable-queue which might be from dhowells@redhat.com are

queue-3.18/keys-fix-asn.1-indefinite-length-object-parsing.patch
queue-3.18/asn.1-fix-non-match-detection-failure-on-data-overrun.patch