Re: [tor-dev] Remove NULL checks for *_free() calls

On Sun, Aug 30, 2015 at 8:13 PM, Michael McConville mmcconv1@sccs.swarthmore.edu wrote:

free() is specified to be NULL-safe, and I don't know of any implementations that violate this.

I think those NULL checks are meant to avoid double-free bugs. If you assign NULL to a pointer after you free it and check all pointers before free, you avoid trying to free it again.

Like there:

error:

• if (x509) {
• X509_free(x509);
• x509 = NULL;
• }

But you did find some places they forgot to assign NULL after free.

Here's a fun exercise: use Coccinelle to find and patch those.

http://coccinelle.lip6.fr/

A semantic patch might look like this:

@@ identifier f =~ "free"; expression x; @@ f(x); + x = NULL;

Happy hacking!

Mansour