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From: kernelnewbies-bounces@xxxxxxxxxxxxxxxxx [mailto:kernelnewbies-bounces@xxxxxxxxxxxxxxxxx]
On Behalf Of lx 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) { /* */ 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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