chacha20/poly1305: make sure to clear the buffer at correct position

The offset to the memory to clear was incorrect, causing a heap buffer
overflow.

CVE-2016-7054

Thanks to Robert Święcki for reporting this

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit b8e4011fb26364e44230946b87ab38cc1c719aae)

diff --git a/crypto/evp/e_chacha20_poly1305.c b/crypto/evp/e_chacha20_poly1305.c
index cf4097ba5daf1e231b2e75d8d8c32aa0de9df4fe..952bd3fca781196a595e43d70fb9a76c3fd072a7 100644 (file)
--- a/crypto/evp/e_chacha20_poly1305.c
+++ b/crypto/evp/e_chacha20_poly1305.c
@@ -299,7 +299,7 @@ static int chacha20_poly1305_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
                 memcpy(out, actx->tag, POLY1305_BLOCK_SIZE);
             } else {
                 if (CRYPTO_memcmp(temp, in, POLY1305_BLOCK_SIZE)) {
                 memcpy(out, actx->tag, POLY1305_BLOCK_SIZE);
             } else {
                 if (CRYPTO_memcmp(temp, in, POLY1305_BLOCK_SIZE)) {

-                    memset(out, 0, plen);
+                    memset(out - plen, 0, plen);

                     return -1;
                 }
             }
                     return -1;
                 }
             }