Re: Possible segfault introduced in commit.c

[René Scharfe <rene.scharfe@xxxxxxxxxxxxxx>]

Am 25.04.2012 13:14, schrieb Jeff King:
> On Wed, Apr 25, 2012 at 12:59:28AM -0700, Michael Mueller wrote:
>
> > As you might already know, we analyze git regularly with Sentry (our
> > static analysis tool).  Today it picked up a new NULL pointer
> > dereference in commit.c:366:
> >
> >      void commit_list_reverse(struct commit_list **list_p)
> >      {
> >          struct commit_list *prev = NULL, *curr = *list_p, *next;
> >
> >          if (!list_p)
> >              return;
> >          /* function continues... */
> >      }
> >
> > list_p is dereferenced on the first line, then tested for NULL on
> > the very next statement.  If it's possible that list_p is NULL, this
> > will be a segfault.  If it can't be NULL, then the check is
> > unnecessary (and probably misleading).
>
> Yes, you're right. There is only one caller currently, and it can never
> be NULL (it passes the address-of a pointer variable). I think dropping
> the NULL-check is the right thing; even an empty list will still have a
> pointer to its NULL head.

More often then not, a mistake like that is surrounded by other issues. 
 No, I didn't put it there intentionally to prove this point. ;-)

Having to reverse the list at all is unfortunate and I only did that 
because I thought appending would be more complicated and because we are 
going to replace the linked list with a different data structure soon 
anyway.  Turns out appending is easy.  Patches to follow.

René
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