Fix test used for not-in-place CBC mode.
With NO_ASM defined, the recent AEAD changes broke the tests. The
problem is that the generic CBC mode code tests whether in != out and
omits to save the IV, assuming that it'll be able to read the old
ciphertext block.
However, consider the case where out = in - 16:
1 2 3 4
|-------|-------|------|-------|
^ ^
| |
out in
First time around, 1 = decrypt(2) ^ iv and everything is fine, because
the IV was preconfigured. However, the next iteration of the loop sets
2 = decrypt(3) and tries to XOR it with the contents of the previous
ciphertext block… from 2.
Change-Id: Ibabff430704fad246de132b4d6d514f6a0362734
diff --git a/crypto/modes/cbc.c b/crypto/modes/cbc.c
index ba4805b..f0889ef 100644
--- a/crypto/modes/cbc.c
+++ b/crypto/modes/cbc.c
@@ -121,7 +121,10 @@
assert(in && out && key && ivec);
- if (in != out) {
+ const uintptr_t inptr = (uintptr_t) in;
+ const uintptr_t outptr = (uintptr_t) out;
+
+ if ((inptr >= 32 && outptr <= inptr - 32) || inptr < outptr) {
const uint8_t *iv = ivec;
if (STRICT_ALIGNMENT &&
