2017-10-29 01:48:53 -04:00
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From 23c8a812dc3c621009e4f0e5342aa4e2ede1ceaa Mon Sep 17 00:00:00 2001
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From: David Howells <dhowells@redhat.com>
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Date: Tue, 23 Feb 2016 11:03:12 +0000
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2017-11-07 17:32:46 -05:00
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Subject: KEYS: Fix ASN.1 indefinite length object parsing
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2017-10-29 01:48:53 -04:00
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This fixes CVE-2016-0758.
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In the ASN.1 decoder, when the length field of an ASN.1 value is extracted,
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it isn't validated against the remaining amount of data before being added
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to the cursor. With a sufficiently large size indicated, the check:
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datalen - dp < 2
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may then fail due to integer overflow.
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Fix this by checking the length indicated against the amount of remaining
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data in both places a definite length is determined.
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Whilst we're at it, make the following changes:
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(1) Check the maximum size of extended length does not exceed the capacity
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of the variable it's being stored in (len) rather than the type that
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variable is assumed to be (size_t).
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(2) Compare the EOC tag to the symbolic constant ASN1_EOC rather than the
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integer 0.
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(3) To reduce confusion, move the initialisation of len outside of:
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for (len = 0; n > 0; n--) {
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since it doesn't have anything to do with the loop counter n.
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Signed-off-by: David Howells <dhowells@redhat.com>
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Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
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Acked-by: David Woodhouse <David.Woodhouse@intel.com>
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Acked-by: Peter Jones <pjones@redhat.com>
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---
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lib/asn1_decoder.c | 16 +++++++++-------
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1 file changed, 9 insertions(+), 7 deletions(-)
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diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c
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2017-11-07 17:32:46 -05:00
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index 2b3f46c..5545229 100644
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2017-10-29 01:48:53 -04:00
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--- a/lib/asn1_decoder.c
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+++ b/lib/asn1_decoder.c
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2017-11-07 17:32:46 -05:00
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@@ -74,7 +74,7 @@ next_tag:
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2017-10-29 01:48:53 -04:00
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/* Extract a tag from the data */
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tag = data[dp++];
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- if (tag == 0) {
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+ if (tag == ASN1_EOC) {
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/* It appears to be an EOC. */
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if (data[dp++] != 0)
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goto invalid_eoc;
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2017-11-07 17:32:46 -05:00
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@@ -96,10 +96,8 @@ next_tag:
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2017-10-29 01:48:53 -04:00
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/* Extract the length */
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len = data[dp++];
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- if (len <= 0x7f) {
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- dp += len;
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- goto next_tag;
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- }
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+ if (len <= 0x7f)
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+ goto check_length;
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if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
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/* Indefinite length */
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2017-11-07 17:32:46 -05:00
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@@ -110,14 +108,18 @@ next_tag:
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2017-10-29 01:48:53 -04:00
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}
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n = len - 0x80;
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- if (unlikely(n > sizeof(size_t) - 1))
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+ if (unlikely(n > sizeof(len) - 1))
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goto length_too_long;
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if (unlikely(n > datalen - dp))
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goto data_overrun_error;
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- for (len = 0; n > 0; n--) {
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+ len = 0;
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+ for (; n > 0; n--) {
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len <<= 8;
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len |= data[dp++];
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}
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+check_length:
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+ if (len > datalen - dp)
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+ goto data_overrun_error;
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dp += len;
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goto next_tag;
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2017-11-07 17:32:46 -05:00
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--
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cgit v1.1
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