crypto: aesni - fix memory usage in GCM decryption

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@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
index 947c6bf52c330452cfb7ac4a19d368f68f4e4509..54f60ab41c63025fd2cb42e5579df7f69c3d9b60 100644 (file)
--- a/arch/x86/crypto/aesni-intel_glue.c
+++ b/arch/x86/crypto/aesni-intel_glue.c
@@ -1155,7 +1155,7 @@ 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);
@@ -1180,7 +1180,7 @@ 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;