From 32cc2479b473c49ce869e57fded7e9a77b695c0d Mon Sep 17 00:00:00 2001 From: "Dr. Stephen Henson" Date: Thu, 7 Feb 2013 21:06:37 +0000 Subject: [PATCH] Fix IV check and padding removal. Fix the calculation that checks there is enough room in a record after removing padding and optional explicit IV. (by Steve) For AEAD remove the correct number of padding bytes (by Andy) --- ssl/s3_cbc.c | 33 ++++++++++++--------------------- 1 file changed, 12 insertions(+), 21 deletions(-) diff --git a/ssl/s3_cbc.c b/ssl/s3_cbc.c index ce77acd..0f60507 100644 --- a/ssl/s3_cbc.c +++ b/ssl/s3_cbc.c @@ -139,31 +139,22 @@ int tls1_cbc_remove_padding(const SSL* s, unsigned mac_size) { unsigned padding_length, good, to_check, i; - const char has_explicit_iv = - s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION; - const unsigned overhead = 1 /* padding length byte */ + - mac_size + - (has_explicit_iv ? block_size : 0); - - /* These lengths are all public so we can test them in non-constant - * time. */ - if (overhead > rec->length) - return 0; - - /* We can always safely skip the explicit IV. We check at the beginning - * of this function that the record has at least enough space for the - * IV, MAC and padding length byte. (These can be checked in - * non-constant time because it's all public information.) So, if the - * padding was invalid, then we didn't change |rec->length| and this is - * safe. If the padding was valid then we know that we have at least - * overhead+padding_length bytes of space and so this is still safe - * because overhead accounts for the explicit IV. */ - if (has_explicit_iv) + const unsigned overhead = 1 /* padding length byte */ + mac_size; + /* Check if version requires explicit IV */ + if (s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION) { + /* These lengths are all public so we can test them in + * non-constant time. + */ + if (overhead + block_size > rec->length) + return 0; + /* We can now safely skip explicit IV */ rec->data += block_size; rec->input += block_size; rec->length -= block_size; } + else if (overhead > rec->length) + return 0; padding_length = rec->data[rec->length-1]; @@ -190,7 +181,7 @@ int tls1_cbc_remove_padding(const SSL* s, if (EVP_CIPHER_flags(s->enc_read_ctx->cipher)&EVP_CIPH_FLAG_AEAD_CIPHER) { /* padding is already verified */ - rec->length -= padding_length; + rec->length -= padding_length + 1; return 1; } -- 1.8.1.2