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
