Hi All,
Using OpenSSL 1.0.2g, I have written a code to generate the hash of a file
in an embeddded device having linux OS and low memory capacity and the
files are generally of size 44 MB or more. The first time or even the
second time on some occasions, the hash of any file is successfully
generated. On the 3rd or 4th time (possibly due to lack of memory/memory
leak), the system reboots before the hash can be generated. After restart,
the same thing happens when the previous steps are repeated.
The stats below shows the memory usage before and after computing the hash.
*root@at91sam9m10g45ek:~# free*
* total used free shared
buff/cache available*
*Mem: 252180 13272 223048 280 15860
230924*
*Swap: 0 0 0*
*After computing hash :-*
*root@at91sam9m10g45ek:~# free*
* total used free shared
buff/cache available*
*Mem: 252180 13308 179308 280 59564
230868*
*Swap: 0 0 0*
Buff/cache increases by almost 44MB (same as file size) everytime I
generate the hash and free decreases. I believe the file is being loaded
into buffer and not being freed.
I am using the below code to compute the message digest. This code is part
of a function ComputeHash and the file pointer here is fph.
* EVP_add_digest(EVP_sha256());*
* md = EVP_get_digestbyname("sha256");*
* if(!md) {*
* printf("Unknown message digest \n");*
* exit(1);*
* }*
* printf("Message digest algorithm successfully loaded\n");*
* mdctx = EVP_MD_CTX_create();*
* EVP_DigestInit_ex(mdctx, md, NULL);*
* // Reading data to array of unsigned chars *
* long long int bytes_read = 0;*
* printf("FILE size of the file to be hashed is %ld",filesize); *
* //reading image file in chunks below and fph is the file pointer to the
44MB file*
* while ((bytes_read = fread (message_data, 1, BUFFER_SIZE, fph)) != 0)*
* EVP_DigestUpdate(mdctx, message_data, bytes_read);*
* EVP_DigestFinal_ex(mdctx, hash_data.md_value, &hash_data.md_len);*
* printf("\n%d\n",EVP_MD_CTX_size(mdctx));*
* printf("\n%d\n",EVP_MD_CTX_type(mdctx));*
* hash_data.md_type=EVP_MD_CTX_type(mdctx);*
* EVP_MD_CTX_destroy(mdctx);*
* //fclose(fp);*
* printf("Generated Digest is:\n ");*
* for(i = 0; i < hash_data.md_len; i++)*
* printf("%02x", hash_data.md_value[i]);*
* printf("\n");*
* EVP_cleanup();*
* return hash_data;*
In the the code below, I have done fclose(fp)
*verify_hash=ComputeHash(fp,size1);*
*fclose(fp);*
I believe that instead of loading the entire file all at once I am reading
the 44MB file in chunks and computing the hash using the piece of code
below: (fph is the file pointer)
*while ((bytes_read = fread (message_data, 1, BUFFER_SIZE, fph)) != 0)*
* EVP_DigestUpdate(mdctx, message_data, bytes_read);*
Where I am going wrong? How can I free the buff/cache after computation of
message digest? Please suggest ways to tackle this.
Thanks and Regards,
Prithiraj
