Same concerns are raised while trying to gain performance by reusing the SSL structure, instead of reallocating it for new connection establishment. Using SSL_clear(SSL *s), as part of the reuse flow, involves a call to OPENSSL_cleanse.
Following OPENSSL_cleanse with a call to memset() may result with performance degradation. Are the OPENSSL_cleanse replacements required in all cases ? Should we be able to dynamically define which behavior is preferable ? Yoram. -----Original Message----- From: Ben Laurie [mailto:[EMAIL PROTECTED]] Sent: Mon, December 09, 2002 12:50 PM To: [EMAIL PROTECTED] Subject: Re: Concerns about the use of OPENSSL_cleanse() Jeffrey Altman wrote: > I think we need to take a very close look at the situations when it is > safe to replace memset(buf,0,sizeof(buf)) with > OPENSSL_cleanse(buf,sizeof(buf)). > It is clearly safe to make this replacement when the buffer is a stack > allocation because there can be no future use of the data can take > place. So there is no functional difference between a buffer filled > with zeros and a buffer filled with garbage data. > > However, this is not true for data structures that are located on the > heap. In many cases OpenSSL provides functions that allow a buffer to > be reused: XXX_init(), XXX_cleanup(), XXX_free(). This is true for > several data structures. By replacing memset() with OPENSSL_cleanse() > in the XXX_cleanup() function we have a problem when the data structure > contains pointers to additional heap allocations. > One case that I found a problem with is: > > . application allocates X509_STORE_CTX and initializes it with > X509_STORE_CTX_init(). > . application calls X509_STORE_CTX_cleanup() which in turn calls > OPENSSL_cleanse() > > . application calls X509_STORE_CTX_free() which in turn calls > X509_STORE_CTX_cleanup(). > This results in an exception because the ex_data field is a struct that > contains pointers to memory allocations. Due to the OPENSSL_cleanse() > call the pointer values are garbage non-NULL values. An attempt is made > to free the memory. This causes an exception. > > This is going to require careful examination to find all of the places > where pointers need to be set to NULL after or during a cleanse operation. OPENSSL_cleanse() should be followed by a memset()? OTOH, if the result of memset() is used, then it can't be optimised away... Cheers, Ben. -- http://www.apache-ssl.org/ben.html http://www.thebunker.net/ "There is no limit to what a man can do or how far he can go if he doesn't mind who gets the credit." - Robert Woodruff ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List [EMAIL PROTECTED] Automated List Manager [EMAIL PROTECTED] ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List [EMAIL PROTECTED] Automated List Manager [EMAIL PROTECTED]
