CMAC with AES_ECB crashes if custom allocator is installed #319

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opened 2019-11-12 05:37:18 -06:00 by guidovranken · 2 comments

guidovranken commented

2019-11-12 05:37:18 -06:00

(Migrated from github.com)

Description

If a custom allocator is installed, CMAC with AES_ECB will crash.

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <mbedtls/cmac.h>
#include <mbedtls/platform.h>

#define CF_CHECK_EQ(expr, res) if ( (expr) != (res) ) { goto end; }
#define CF_CHECK_NE(expr, res) if ( (expr) == (res) ) { goto end; }

static void* mbedTLS_custom_calloc(size_t A, size_t B) {
    return malloc(A*B);
}

static void mbedTLS_custom_free(void* ptr) {
    free(ptr);
}

int main(void)
{    
    const mbedtls_cipher_info_t *cipher_info = NULL;
    const uint8_t key[32];
    const uint8_t cleartext[16];
    uint8_t out[1024];

    if ( mbedtls_platform_set_calloc_free(mbedTLS_custom_calloc, mbedTLS_custom_free) != 0 ) {
        abort();
    }

    CF_CHECK_NE(cipher_info = mbedtls_cipher_info_from_type(MBEDTLS_CIPHER_AES_256_ECB), NULL);
    CF_CHECK_EQ(mbedtls_cipher_cmac(cipher_info, key, sizeof(key) * 8, cleartext, sizeof(cleartext), out), 0);

end:

    return 0;
}

Issue request type

[ ] Question
[ ] Enhancement
[x] Bug

### Description If a custom allocator is installed, CMAC with AES_ECB will crash. ```c #include <stdint.h> #include <stdlib.h> #include <stdio.h> #include <mbedtls/cmac.h> #include <mbedtls/platform.h> #define CF_CHECK_EQ(expr, res) if ( (expr) != (res) ) { goto end; } #define CF_CHECK_NE(expr, res) if ( (expr) == (res) ) { goto end; } static void* mbedTLS_custom_calloc(size_t A, size_t B) { return malloc(A*B); } static void mbedTLS_custom_free(void* ptr) { free(ptr); } int main(void) { const mbedtls_cipher_info_t *cipher_info = NULL; const uint8_t key[32]; const uint8_t cleartext[16]; uint8_t out[1024]; if ( mbedtls_platform_set_calloc_free(mbedTLS_custom_calloc, mbedTLS_custom_free) != 0 ) { abort(); } CF_CHECK_NE(cipher_info = mbedtls_cipher_info_from_type(MBEDTLS_CIPHER_AES_256_ECB), NULL); CF_CHECK_EQ(mbedtls_cipher_cmac(cipher_info, key, sizeof(key) * 8, cleartext, sizeof(cleartext), out), 0); end: return 0; } ``` ### Issue request type [ ] Question [ ] Enhancement [x] Bug

gilles-peskine-arm commented

2019-11-12 10:19:22 -06:00

(Migrated from github.com)

I can't reproduce this crash.

# your code in a.c
$ scripts/config.pl set MBEDTLS_PLATFORM_MEMORY
$ make
$ gcc -I include -L library -O -Wall -Wextra -c a.c -lmbedcrypto && ./a.out && echo ok
Current use: 0 blocks / 0 bytes, max: 0 blocks / 0 bytes (total 0 bytes), alloc / free: 0 / 0
All memory de-allocated in stack buffer
ok

But I do see a bug in your code: mbedTLS_custom_calloc should use calloc, not malloc (or use malloc and then memset to 0). The library assumes that the allocator returns memory with a content of all-bits-zero. Does the code work for you if you properly initialize the memory to 0?

I can't reproduce this crash. ``` # your code in a.c $ scripts/config.pl set MBEDTLS_PLATFORM_MEMORY $ make $ gcc -I include -L library -O -Wall -Wextra -c a.c -lmbedcrypto && ./a.out && echo ok Current use: 0 blocks / 0 bytes, max: 0 blocks / 0 bytes (total 0 bytes), alloc / free: 0 / 0 All memory de-allocated in stack buffer ok ``` But I do see a bug in your code: `mbedTLS_custom_calloc` should use `calloc`, not `malloc` (or use `malloc` and then `memset` to 0). The library assumes that the allocator returns memory with a content of all-bits-zero. Does the code work for you if you properly initialize the memory to 0?

guidovranken commented

2019-11-12 10:49:43 -06:00

(Migrated from github.com)