Re: [PATCH] CryptoPkg/BaseCryptLib: fix NULL dereference (CVE-2019-14584)


Wang, Jian J
 

Laszlo,

-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Laszlo Ersek
Sent: Tuesday, October 20, 2020 3:13 AM
To: devel@edk2.groups.io; Wang, Jian J <jian.j.wang@...>
Cc: Lu, XiaoyuX <xiaoyux.lu@...>; Jiang, Guomin
<guomin.jiang@...>; Yao, Jiewen <jiewen.yao@...>
Subject: Re: [edk2-devel] [PATCH] CryptoPkg/BaseCryptLib: fix NULL
dereference (CVE-2019-14584)

On 10/16/20 07:14, Wang, Jian J wrote:
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1914

AuthenticodeVerify() calls OpenSSLs d2i_PKCS7() API to parse asn encoded
signed authenticode pkcs#7 data. when this successfully returns, a type
check is done by calling PKCS7_type_is_signed() and then
Pkcs7->d.sign->contents->type is used. It is possible to construct an asn1
blob that successfully decodes and have d2i_PKCS7() return a valid pointer
and have PKCS7_type_is_signed() also return success but have Pkcs7->d.sign
be a NULL pointer.

Looking at how PKCS7_verify() [inside of OpenSSL] implements checking for
pkcs7 structs it does the following:
- call PKCS7_type_is_signed()
- call PKCS7_get_detached()
Looking into how PKCS7_get_detatched() is implemented, it checks to see if
p7->d.sign is NULL or if p7->d.sign->contents->d.ptr is NULL.

As such, the fix is to do the same as OpenSSL after calling d2i_PKCS7().
- Add call to PKS7_get_detached() to existing error handling

Cc: Xiaoyu Lu <xiaoyux.lu@...>
Cc: Guomin Jiang <guomin.jiang@...>
Cc: Jiewen Yao <jiewen.yao@...>
Cc: Laszlo Ersek <lersek@...>
Signed-off-by: Jian J Wang <jian.j.wang@...>
Reviewed-by: Laszlo Ersek <lersek@...>
---
CryptoPkg/Library/BaseCryptLib/Pk/CryptAuthenticode.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CryptoPkg/Library/BaseCryptLib/Pk/CryptAuthenticode.c
b/CryptoPkg/Library/BaseCryptLib/Pk/CryptAuthenticode.c
index 2772b1e2be..ae0ee61fb6 100644
--- a/CryptoPkg/Library/BaseCryptLib/Pk/CryptAuthenticode.c
+++ b/CryptoPkg/Library/BaseCryptLib/Pk/CryptAuthenticode.c
@@ -9,7 +9,7 @@
AuthenticodeVerify() will get PE/COFF Authenticode and will do basic check
for
data structure.

-Copyright (c) 2011 - 2015, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2011 - 2019, Intel Corporation. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent

**/
It's probably best to bump the (C) date to 2020; if you must update the
(C) line in the first place.

Otherwise, this patch seems identical to what I reviewed in
<https://bugzilla.tianocore.org/show_bug.cgi?id=1914#c6>, so my R-b stands.
Thanks for catching this. I'll update it before pushing.

Regards,
Jian

Thanks
Laszlo

@@ -100,7 +100,7 @@ AuthenticodeVerify (
//
// Check if it's PKCS#7 Signed Data (for Authenticode Scenario)
//
- if (!PKCS7_type_is_signed (Pkcs7)) {
+ if (!PKCS7_type_is_signed (Pkcs7) || PKCS7_get_detached (Pkcs7)) {
goto _Exit;
}




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