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Fix unintended sign extension

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The function CRYPTO_128_unwrap_pad uses an 8 byte AIV (Alternative Initial
Value). The least significant 4 bytes of this is placed into the local
variable |ptext_len|. This is done as follows:

    ptext_len = (aiv[4] << 24) | (aiv[5] << 16) | (aiv[6] << 8) | aiv[7];

aiv[4] is an unsigned char, but (aiv[4] << 24) is promoted to a *signed*
int - therefore we could end up shifting into the sign bit and end up with
a negative value. |ptext_len| is a size_t (typically 64-bits). If the
result of the shifts is negative then the upper bits of |ptext_len| will
all be 1.

This commit fixes the issue by explicitly casting to an unsigned int.

Reviewed-by: Richard Levitte <levitte@openssl.org>
This commit is contained in:
Matt Caswell 2015-03-12 15:59:07 +00:00
parent dfef52f6f2
commit 3475c7a185
1 changed files with 4 additions and 1 deletions
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5
crypto/modes/wrap128.c
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@ -350,7 +350,10 @@ size_t CRYPTO_128_unwrap_pad(void *key, const unsigned char *icv,
* LSB(32,AIV).
*/
ptext_len = (aiv[4] << 24) | (aiv[5] << 16) | (aiv[6] << 8) | aiv[7];
ptext_len = ((unsigned int)aiv[4] << 24)
| ((unsigned int)aiv[5] << 16)
| ((unsigned int)aiv[6] << 8)
| (unsigned int)aiv[7];
if (8 * (n - 1) >= ptext_len || ptext_len > 8 * n) {
OPENSSL_cleanse(out, inlen);
return 0;