linux-kernel - [PATCH 3.12 061/155] crypto: aesni - fix memory usage in GCM decryption

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Date:	Tue,  7 Apr 2015 14:50:30 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Stephan Mueller <smueller@...onox.de>,
	Tadeusz Struk <tadeusz.struk@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 061/155] crypto: aesni - fix memory usage in GCM decryption

From: Stephan Mueller <smueller@...onox.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit ccfe8c3f7e52ae83155cb038753f4c75b774ca8a upstream.

The kernel crypto API logic requires the caller to provide the
length of (ciphertext || authentication tag) as cryptlen for the
AEAD decryption operation. Thus, the cipher implementation must
calculate the size of the plaintext output itself and cannot simply use
cryptlen.

The RFC4106 GCM decryption operation tries to overwrite cryptlen memory
in req->dst. As the destination buffer for decryption only needs to hold
the plaintext memory but cryptlen references the input buffer holding
(ciphertext || authentication tag), the assumption of the destination
buffer length in RFC4106 GCM operation leads to a too large size. This
patch simply uses the already calculated plaintext size.

In addition, this patch fixes the offset calculation of the AAD buffer
pointer: as mentioned before, cryptlen already includes the size of the
tag. Thus, the tag does not need to be added. With the addition, the AAD
will be written beyond the already allocated buffer.

Note, this fixes a kernel crash that can be triggered from user space
via AF_ALG(aead) -- simply use the libkcapi test application
from [1] and update it to use rfc4106-gcm-aes.

Using [1], the changes were tested using CAVS vectors to demonstrate
that the crypto operation still delivers the right results.

[1] http://www.chronox.de/libkcapi.html

CC: Tadeusz Struk <tadeusz.struk@...el.com>
Signed-off-by: Stephan Mueller <smueller@...onox.de>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/crypto/aesni-intel_glue.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
index f89e7490d303..990c9699b662 100644
--- a/arch/x86/crypto/aesni-intel_glue.c
+++ b/arch/x86/crypto/aesni-intel_glue.c
@@ -989,7 +989,7 @@ static int __driver_rfc4106_decrypt(struct aead_request *req)
 		src = kmalloc(req->cryptlen + req->assoclen, GFP_ATOMIC);
 		if (!src)
 			return -ENOMEM;
-		assoc = (src + req->cryptlen + auth_tag_len);
+		assoc = (src + req->cryptlen);
 		scatterwalk_map_and_copy(src, req->src, 0, req->cryptlen, 0);
 		scatterwalk_map_and_copy(assoc, req->assoc, 0,
 			req->assoclen, 0);
@@ -1014,7 +1014,7 @@ static int __driver_rfc4106_decrypt(struct aead_request *req)
 		scatterwalk_done(&src_sg_walk, 0, 0);
 		scatterwalk_done(&assoc_sg_walk, 0, 0);
 	} else {
-		scatterwalk_map_and_copy(dst, req->dst, 0, req->cryptlen, 1);
+		scatterwalk_map_and_copy(dst, req->dst, 0, tempCipherLen, 1);
 		kfree(src);
 	}
 	return retval;
-- 
2.3.4

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