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

[Mansour Moufid <mansourmoufid@xxxxxxxxx>]

On Sun, Aug 30, 2015 at 8:13 PM, Michael McConville
<mmcconv1@xxxxxxxxxxxxxxxxxxx> 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
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