AW: OpenSSL hash memory leak

Georg Höllrigl georg.hoellrigl at
Sat Feb 23 21:44:58 UTC 2019



I guess you’re not seeing a memory leak, but just normal behaviour of linux file system cache.

Buff/cache is keeping files in memory that were least accessed as long as not needed by other stuff.

You don’t need to free the buffer/cache, because linux does that automatically, when memory is needed.


Kind Regards,



Von: openssl-users <openssl-users-bounces at> Im Auftrag von prithiraj das
Gesendet: 23 February 2019 18:25
An: Jordan Brown <openssl at>
Cc: openssl-users at
Betreff: Re: OpenSSL hash memory leak



This is how I have initialized my variables:-


EVP_MD_CTX *mdctx;

const EVP_MD *md;

int i;

HASH hash_data;

unsigned char message_data[BUFFER_SIZE];


BUFFER_SIZE has been defined as 131072

and HASH is my hash structure defined to hold the message digest, message digest length and message digest type


On Sat, 23 Feb 2019 at 00:17, Jordan Brown <openssl at <mailto:openssl at> > wrote:

The most obvious question is "how are you allocating your message_data buffer?".  You don't show that.


On 2/22/2019 2:27 AM, prithiraj das wrote:


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 at at91sam9m10g45ek:~# free

                      total        used          free         shared    buff/cache   available

Mem:         252180       13272      223048         280          15860          230924

Swap:                0           0               0


After computing hash :-

root at 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.



 md = EVP_get_digestbyname("sha256");


 if(!md) {

        printf("Unknown message digest \n");



 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("Generated Digest is:\n ");

 for(i = 0; i < hash_data.md_len; i++)

        printf("%02x", hash_data.md_value[i]);



         return hash_data;


In the the code below, I have done 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,




Jordan Brown, Oracle ZFS Storage Appliance, Oracle Solaris

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