Re: SHA-1 hash calculate in Kernel.

[Bernd Petrovitsch]

On Fre, 2015-08-28 at 15:36 +0800, lx wrote:
[...]
 //way 2
 /*
 char *plaintext = kmalloc(sizeof(char), GFP_KERNEL);
 plaintext = c;

I don't think that this line doesn't give any warning ...

Kind regards,
Bernd
-- 
I dislike type abstraction if it has no real reason. And saving
on typing is not a good reason - if your typing speed is the main
issue when you're coding, you're doing something seriously wrong.
- Linus Torvalds


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Re: SHA-1 hash calculate in Kernel.

[Bjørn Mork]

lx lxlenovos...@gmail.com writes:

 hi all:
   I built a module for calculate the SHA-1. The code is:
 ##
 #include linux/init.h
 #include linux/module.h
 #include linux/kernel.h
 #include linux/crypto.h
 #include linux/err.h
 #include linux/scatterlist.h
 MODULE_LICENSE(Dual BSD/GPL);

 #define SHA1_LENGTH 20

 static int hello_init(void)
 {
 /*
  * http://lxr.oss.org.cn/source/fs/ecryptfs/crypto.c?v=2.6.30
  */
 struct scatterlist sg;
 struct hash_desc desc;

 //way 1
 /*
 char *plaintext = c;
 size_t len = strlen(plaintext);
 */

 //way 2
 /*
 char *plaintext = kmalloc(sizeof(char), GFP_KERNEL);
 plaintext = c;
 size_t len = 1;
 */

 // way 3.
 /*
 char plaintext[1] = {'c'};
 size_t len = 1;
 */

 // way 4.
 /*
 char *plaintext = (char *)__get_free_page(GFP_KERNEL);
 memcpy(plaintext, c, 1);
 size_t len = 1;
 */

 int rc = 0;
 int i;
 char hashtext[SHA1_LENGTH];

 memset(hashtext, 0x00, SHA1_LENGTH);
 printk(KERN_INFO sha1: %s\n, __FUNCTION__);

 sg_init_one(sg, plaintext, len);
 desc.tfm = crypto_alloc_hash(sha1, 0, CRYPTO_ALG_ASYNC);
 desc.flags = 0;

 rc = crypto_hash_init(desc);
 if (rc) {
 printk(KERN_ERR %s: Error initializing crypto hash; rc = [%d]\n,
 __func__, rc);
 goto out;
 }
 rc = crypto_hash_update(desc, sg, len);
 if (rc) {
 printk(KERN_ERR %s: Error updating crypto hash; rc = [%d]\n,
 __func__, rc);
 goto out;
 }
 rc = crypto_hash_final(desc, hashtext);
 if (rc) {
 printk(KERN_ERR %s: Error finalizing crypto hash; rc = [%d]\n,
 __func__, rc);
 goto out;
 }
 crypto_free_hash(desc.tfm);

 for (i = 0; i  20; i++) {
 printk(KERN_INFO %02x-%d\n, hashtext[i]0xff, i);
 }

 out:
 printk(KERN_INFO end\n);
 return rc;
 }

 static void hello_exit(void)
 {
 printk(KERN_ALERT Goodbye, cruel world\n);
 }

 module_init(hello_init);
 module_exit(hello_exit);
 ##
 I can just get the right result by way 3 and 4, In way 1 and 2 , I get the
 wrong result,

I suggest you add something like this:

printk(KERN_INFO plaintext='%c', len=%zu, valid=%s\n, *plaintext, len, 
virt_addr_valid(plaintext) ? true : false);


and then go figure out the relationship between that and the correct
result :)




Bjørn

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RE: SHA-1 hash calculate in Kernel.

[Jeff Haran]

From: kernelnewbies-boun...@kernelnewbies.org 
[mailto:kernelnewbies-boun...@kernelnewbies.org] On Behalf Of lx
Sent: Friday, August 28, 2015 12:36 AM
To: kernelnewbies
Subject: SHA-1 hash calculate in Kernel.

hi all:
  I built a module for calculate the SHA-1. The code is:
##
#include linux/init.h
#include linux/module.h
#include linux/kernel.h
#include linux/crypto.h
#include linux/err.h
#include linux/scatterlist.h
MODULE_LICENSE(Dual BSD/GPL);

#define SHA1_LENGTH 20

static int hello_init(void)
{
/*
 * http://lxr.oss.org.cn/source/fs/ecryptfs/crypto.c?v=2.6.30
 */
struct scatterlist sg;
struct hash_desc desc;

//way 1
/*
char *plaintext = c;
size_t len = strlen(plaintext);
*/

//way 2
/*
char *plaintext = kmalloc(sizeof(char), GFP_KERNEL);
plaintext = c;
size_t len = 1;
*/

// way 3.
/*
char plaintext[1] = {'c'};
size_t len = 1;
*/

// way 4.
/*
char *plaintext = (char *)__get_free_page(GFP_KERNEL);
memcpy(plaintext, c, 1);
size_t len = 1;
*/

int rc = 0;
int i;
char hashtext[SHA1_LENGTH];

memset(hashtext, 0x00, SHA1_LENGTH);
printk(KERN_INFO sha1: %s\n, __FUNCTION__);

sg_init_one(sg, plaintext, len);
desc.tfm = crypto_alloc_hash(sha1, 0, CRYPTO_ALG_ASYNC);
desc.flags = 0;

rc = crypto_hash_init(desc);
if (rc) {
printk(KERN_ERR %s: Error initializing crypto hash; rc = [%d]\n, 
__func__, rc);
goto out;
}
rc = crypto_hash_update(desc, sg, len);
if (rc) {
printk(KERN_ERR %s: Error updating crypto hash; rc = [%d]\n, 
__func__, rc);
goto out;
}
rc = crypto_hash_final(desc, hashtext);
if (rc) {
printk(KERN_ERR %s: Error finalizing crypto hash; rc = [%d]\n, 
__func__, rc);
goto out;
}
crypto_free_hash(desc.tfm);

for (i = 0; i  20; i++) {
printk(KERN_INFO %02x-%d\n, hashtext[i]0xff, i);
}

out:
printk(KERN_INFO end\n);
return rc;
}

static void hello_exit(void)
{
printk(KERN_ALERT Goodbye, cruel world\n);
}

module_init(hello_init);
module_exit(hello_exit);
##
I can just get the right result by way 3 and 4, In way 1 and 2 , I get the 
wrong result,
I check the result by link: http://www.xorbin.com/tools/sha1-hash-calculator .
Please tell me why? Thank you.

I don’t know why the crypto function isn’t generating the right result in the 
first two cases. Just pointing out that way 1 and way 2 are identical except 
that way 2 leaks the memory that was kmalloc()’ed.  This in way 2 is a pointer 
assignment, not a buffer copy:

plaintext = c;

The big difference it seems between ways 1 and 2 and ways 3 and 4 is in the 
former, plaintext points to a string constant that I believe is going to be 
read only whereas in the latter, plaintext points to r/w memory. Maybe the 
crypto functions need r/w access?

Jeff Haran


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