In the Linux kernel, the following vulnerability has been resolved:
crypto: qce – fix CCM AAD buffer underallocation
The AAD buffer allocated in qce_aead_ccm_prepare_buf_assoclen()
can be smaller than the length later programmed into the DMA
scatterlist.
The allocation size is currently calculated as:
ALIGN(assoclen, 16) + MAX_CCM_ADATA_HEADER_LEN
while the DMA length is set to:
ALIGN(assoclen + adata_header_len, 16)
Since ALIGN() does not distribute over addition, the allocation
can be smaller than the DMA length. For example, when
assoclen = 32 and adata_header_len = 2:
allocation = ALIGN(32, 16) + 6 = 38
DMA length = ALIGN(32 + 2, 16) = 48
As a result, the QCE hardware can read beyond the allocated
buffer while computing the CBC-MAC over the associated data.
The extra bytes are folded into the authentication tag,
resulting in an incorrect tag and causing CCM self-test
failures such as:
alg: aead: ccm-aes-qce encryption test failed (wrong result)
on test vector 8
Fix the allocation by adding the maximum possible AAD header
length before alignment:
ALIGN(assoclen + MAX_CCM_ADATA_HEADER_LEN, 16)
This guarantees that the allocated buffer is large enough
for the fully padded AAD data for all supported header sizes.
