Date: Tue, 27 Nov 2012 12:20:17 GMT From: Jan Mikkelsen <janm@transactionware.com> To: freebsd-gnats-submit@FreeBSD.org Subject: misc/173952: BN_add_word writes one past its buffer when certain values are added to a single word bignum Message-ID: <201211271220.qARCKHNt074770@red.freebsd.org> Resent-Message-ID: <201211271230.qARCU1IE047853@freefall.freebsd.org>
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>Number: 173952
>Category: misc
>Synopsis: BN_add_word writes one past its buffer when certain values are added to a single word bignum
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Nov 27 12:30:00 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator: Jan Mikkelsen
>Release: 9.1-RC3
>Organization:
Transactionware
>Environment:
FreeBSD vanaheim.transactionware.com 9.1-RC3 FreeBSD 9.1-RC3 #0: Sun Nov 25 10:40:45 EST 2012 root@vanaheim.transactionware.com:/home/janm/p4/freebsd-image-std-2011.1/work/base-freebsd/home/janm/p4/freebsd-image-std-2011.1/FreeBSD/src/sys/TW amd64
>Description:
The function BN_add_word() in crypto/bn/bn_word.c can write one word past the end of the memory pointed to by the 'd' member of the BIGNUM struct when adding a word to a single word bignum.
This has been reported to the OpenSSL people.
>How-To-Repeat:
dc(1) is implemented in terms of BN_*. This will reproduce the problem:
janm@gray: dc $ dc
18446744073709551616 18446744073709551616 / ps
dc: big number failure 306b06b: No such file or directory
>Fix:
My patch below. The OpenSSL people have a different patch; they were more comfortable restructuring the code.
--- //depot/vendor/freebsd/9.1-local/src/crypto/openssl/crypto/bn/bn_word.c 2012-08-13 00:32:35.000000000 1000
+++ /data/scratch/janm/p4/freebsd-image-std-2011.1/FreeBSD/src/crypto/openssl/crypto/bn/bn_word.c 2012-08-13 00:32:35.000000000 1000
@@ -145,9 +145,11 @@
return(i);
}
/* Only expand (and risk failing) if it's possibly necessary */
- if (((BN_ULONG)(a->d[a->top - 1] + 1) == 0) &&
- (bn_wexpand(a,a->top+1) == NULL))
- return(0);
+ if (
+ (((a->top == 1) && (BN_MASK2 - w < a->d[0])) ||
+ ((a->top > 1) && ((BN_ULONG)(a->d[a->top - 1] + 1) == 0))) &&
+ (bn_wexpand(a,a->top+1) == NULL))
+ return(0);
i=0;
for (;;)
{
>Release-Note:
>Audit-Trail:
>Unformatted:
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