[PATCH 1/1] tools: use adequate entropy source for initialization vector

[Heinrich Schuchardt]

On 4/11/24 01:46, Mark Kettenis wrote:
>> From: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>> Date: Thu, 11 Apr 2024 01:31:16 +0200
>>
>> The random() function is unsafe to initialize cryptographic data.
>> Use getrandom() which reads from /dev/urandom instead.
>>
>> getrandom() is available on Linux sine release 3.17 and on BSD.
> 
> NACK
> 
> getrandom() isn't evailable on OpenBSD.  Either use getentropy() or
> arc4random_buf() instead.

Thanks for reviewing. arc4random_buf() was added to glibc only in 2022. 
So there might be too many users not using a recent enough Linux distro. 
So I guess getentropy() is a better choice.

Best regards

Heinrich

> 
>> Addresses-Coverity-ID: 312953 Calling risky function
>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>> ---
>>   tools/image-host.c | 36 +++---------------------------------
>>   1 file changed, 3 insertions(+), 33 deletions(-)
>>
>> diff --git a/tools/image-host.c b/tools/image-host.c
>> index b2a0f2e6d16..d30a235baf6 100644
>> --- a/tools/image-host.c
>> +++ b/tools/image-host.c
>> @@ -13,11 +13,11 @@
>>   #include <fdt_region.h>
>>   #include <image.h>
>>   #include <version.h>
>> -
>>   #if CONFIG_IS_ENABLED(FIT_SIGNATURE)
>>   #include <openssl/pem.h>
>>   #include <openssl/evp.h>
>>   #endif
>> +#include <sys/random.h>
>>   
>>   /**
>>    * fit_set_hash_value - set hash value in requested has node
>> @@ -364,36 +364,6 @@ static int fit_image_read_key_iv_data(const char *keydir, const char *key_iv_nam
>>   	return ret;
>>   }
>>   
>> -static int get_random_data(void *data, int size)
>> -{
>> -	unsigned char *tmp = data;
>> -	struct timespec date;
>> -	int i, ret;
>> -
>> -	if (!tmp) {
>> -		fprintf(stderr, "%s: pointer data is NULL\n", __func__);
>> -		ret = -1;
>> -		goto out;
>> -	}
>> -
>> -	ret = clock_gettime(CLOCK_MONOTONIC, &date);
>> -	if (ret) {
>> -		fprintf(stderr, "%s: clock_gettime has failed (%s)\n", __func__,
>> -			strerror(errno));
>> -		goto out;
>> -	}
>> -
>> -	srandom(date.tv_nsec);
>> -
>> -	for (i = 0; i < size; i++) {
>> -		*tmp = random() & 0xff;
>> -		tmp++;
>> -	}
>> -
>> - out:
>> -	return ret;
>> -}
>> -
>>   static int fit_image_setup_cipher(struct image_cipher_info *info,
>>   				  const char *keydir, void *fit,
>>   				  const char *image_name, int image_noffset,
>> @@ -465,8 +435,8 @@ static int fit_image_setup_cipher(struct image_cipher_info *info,
>>   		if (ret < 0)
>>   			goto out;
>>   	} else {
>> -		/* Generate an ramdom IV */
>> -		ret = get_random_data((void *)info->iv, info->cipher->iv_len);
>> +		/* Generate a ramdom initialization vector */
>> +		ret = getrandom((void *)info->iv, info->cipher->iv_len, 0);
>>   	}
>>   
>>    out:
>> -- 
>> 2.43.0
>>
>>