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crypto: aes - Undefined behaviour in crypto_aes_expand_key 

It's undefined behaviour in C to write outside the bounds of an array.
The key expansion routine takes a shortcut of creating 8 words at a
time, but this creates 4 additional words which don't fit in the array.

As everyone is hopefully now aware, GCC is at liberty to make any
assumptions and optimisations it likes in situations where it can
detect that UB has occured, up to and including nasal demons, and
as the indices being accessed in the array are trivially calculable,
it's rash to invite gcc to do take any liberties at all.

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Phil Carmody 2009-07-24 13:59:17 +08:00 committed by Herbert Xu
parent 0044f3eda9
commit 7b4ffcf953
1 changed files with 7 additions and 2 deletions
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9
crypto/aes_generic.c
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@ -1174,7 +1174,7 @@ EXPORT_SYMBOL_GPL(crypto_il_tab);
ctx->key_enc[6 * i + 11] = t; \
} while (0)
#define loop8(i) do { \
#define loop8tophalf(i) do { \
t = ror32(t, 8); \
t = ls_box(t) ^ rco_tab[i]; \
t ^= ctx->key_enc[8 * i]; \
@ -1185,6 +1185,10 @@ EXPORT_SYMBOL_GPL(crypto_il_tab);
ctx->key_enc[8 * i + 10] = t; \
t ^= ctx->key_enc[8 * i + 3]; \
ctx->key_enc[8 * i + 11] = t; \
} while (0)
#define loop8(i) do { \
loop8tophalf(i); \
t = ctx->key_enc[8 * i + 4] ^ ls_box(t); \
ctx->key_enc[8 * i + 12] = t; \
t ^= ctx->key_enc[8 * i + 5]; \
@ -1245,8 +1249,9 @@ int crypto_aes_expand_key(struct crypto_aes_ctx *ctx, const u8 *in_key,
ctx->key_enc[5] = le32_to_cpu(key[5]);
ctx->key_enc[6] = le32_to_cpu(key[6]);
t = ctx->key_enc[7] = le32_to_cpu(key[7]);
for (i = 0; i < 7; ++i)
for (i = 0; i < 6; ++i)
loop8(i);
loop8tophalf(i);
break;
}