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tpm2: Add asserts to silence compiler warning due to -Wstringop-overflow=

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The following error occurrs on Fedora build servers. To silence the
compiler warning add runtime asserts:

tpm2/crypto/openssl/CryptCmac.c: In function 'CryptCmacEnd':
tpm2/crypto/openssl/CryptCmac.c:194:48: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
  194 |             subkey.t.buffer[subkey.t.size - 1] ^= xorVal;
      |                                                ^
tpm2/TpmTypes.h:1477:33: note: at offset -1 into destination object 'buffer' of size 16
 1477 |         BYTE                    buffer[MAX_SYM_BLOCK_SIZE];
      |                                 ^
lto1: all warnings being treated as errors

In CryptCmacStart the following initialization is done:

cState->iv.t.size = CryptGetSymmetricBlockSize(def->algorithm, def->keyBits.sym);

Also ensure that CryptGetSymmetricBlockSize in this case also always returns
a valid size to the TPM2B_IV that it is initializing, which would be the root
cause of any error.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
This commit is contained in:
Stefan Berger 2024-12-06 09:56:51 -05:00 committed by Stefan Berger
parent 5e08ef1f53
commit e0dceb11e5
1 changed files with 4 additions and 0 deletions
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4
src/tpm2/crypto/openssl/CryptCmac.c
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@ -92,6 +92,7 @@ CryptCmacStart(
cState->symAlg = def->algorithm;
cState->keySizeBits = def->keyBits.sym;
cState->iv.t.size = CryptGetSymmetricBlockSize(def->algorithm, def->keyBits.sym);
pAssert(cState->iv.t.size > 0 && cState->iv.t.size <= sizeof(cState->iv.t.buffer)); // libtpms added
MemoryCopy2B(&cState->symKey.b, key, sizeof(cState->symKey.t.buffer));
// Set up the dispatch methods for the CMAC
@ -191,6 +192,9 @@ CryptCmacEnd(SMAC_STATES* state, UINT32 outSize, BYTE* outBuffer)
// Now compute K2
xorVal = ((subkey.t.buffer[0] & 0x80) == 0) ? 0 : 0x87;
ShiftLeft(&subkey.b);
MUST_BE(MAX_SYM_BLOCK_SIZE == 16); // libtpms added begin: gcc -Wstringop-overflow=
pAssert(subkey.t.size > 0 &&
subkey.t.size <= sizeof(subkey.t.buffer)); // libtpms added end
subkey.t.buffer[subkey.t.size - 1] ^= xorVal;
}
// XOR the subkey into the IV