crypto: aes - Undefined behaviour in crypto_aes_expand_key (7b4ffcf9) · Commits · 戴 / test

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>

crypto/aes_generic.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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