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evp/evp_enc.c: check for partially[!] overlapping buffers

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in EVP_EncryptUpdate and EVP_DecryptUpdate. It is argued that in
general case it's impossible to provide guarantee that partially[!]
overlapping buffers can be tolerated.

Reviewed-by: Matt Caswell <matt@openssl.org>
This commit is contained in:
Andy Polyakov 2016-06-17 13:55:01 +02:00
parent dca5eeb4d0
commit c3a73daf0a
2 changed files with 44 additions and 1 deletions
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41
crypto/evp/evp_enc.c
View file

@ -8,6 +8,7 @@
*/
#include <stdio.h>
#include <assert.h>
#include "internal/cryptlib.h"
#include <openssl/evp.h>
#include <openssl/err.h>
@ -252,11 +253,48 @@ int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *cipher,
return EVP_CipherInit_ex(ctx, cipher, impl, key, iv, 0);
}
/*
* According to the letter of standard difference between pointers
* is specified to be valid only within same object. This makes
* it formally challenging to determine if input and output buffers
* are not partially overlapping with standard pointer arithmetic.
*/
#ifdef PTRDIFF_T
# undef PTRDIFF_T
#endif
#if defined(OPENSSL_SYS_VMS) && __INITIAL_POINTER_SIZE==64
/*
* Then we have VMS that distinguishes itself by adhering to
* sizeof(size_t)==4 even in 64-bit builds...
*/
# define PTRDIFF_T uint64_t
#else
# define PTRDIFF_T size_t
#endif
static int is_partially_overlapping(const void *ptr1, const void *ptr2,
int len)
{
PTRDIFF_T diff = (PTRDIFF_T)ptr1-(PTRDIFF_T)ptr2;
/*
* Check for partially overlapping buffers. [Binary logical
* operations are used instead of boolean to minimize number
* of conditional branches.]
*/
int condition = (len > 0) & (diff != 0) & ((diff < (PTRDIFF_T)len) |
(diff > (0 - (PTRDIFF_T)len)));
assert(!condition);
return condition;
}
int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
const unsigned char *in, int inl)
{
int i, j, bl;
if (is_partially_overlapping(out, in, inl))
return 0;
if (ctx->cipher->flags & EVP_CIPH_FLAG_CUSTOM_CIPHER) {
i = ctx->cipher->do_cipher(ctx, out, in, inl);
if (i < 0)
@ -370,6 +408,9 @@ int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
int fix_len;
unsigned int b;
if (is_partially_overlapping(out, in, inl))
return 0;
if (ctx->cipher->flags & EVP_CIPH_FLAG_CUSTOM_CIPHER) {
fix_len = ctx->cipher->do_cipher(ctx, out, in, inl);
if (fix_len < 0) {

4
doc/crypto/EVP_EncryptInit.pod
View file

@ -137,7 +137,9 @@ multiple times to encrypt successive blocks of data. The amount
of data written depends on the block alignment of the encrypted data:
as a result the amount of data written may be anything from zero bytes
to (inl + cipher_block_size - 1) so B<out> should contain sufficient
room. The actual number of bytes written is placed in B<outl>.
room. The actual number of bytes written is placed in B<outl>. It also
checks if B<in> and B<out> are partially overlapping, and if they are
0 is returned to indicate failure.
If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts
the "final" data, that is any data that remains in a partial block.