svn commit: r328313 - head/sys/netpfil/pf

[Kristof Provost]

On 25 Jan 2018, at 12:08, Kristof Provost wrote:
> On 25 Jan 2018, at 11:34, Ian Lepore wrote:
>> On Wed, 2018-01-24 at 16:13 -0800, Gleb Smirnoff wrote:
>>> (r328313)
>>> K> @@ -1613,6 +1613,7 @@ int
>>> K>  pf_unlink_state(struct pf_state *s, u_int flags)
>>> K>  {
>>> K>  	struct pf_idhash *ih = &V_pf_idhash[PF_IDHASH(s)];
>>> K> +	int last;
>>> K>  
>>> K>  	if ((flags & PF_ENTER_LOCKED) == 0)
>>> K>  		PF_HASHROW_LOCK(ih);
>>> K> @@ -1653,7 +1654,8 @@ pf_unlink_state(struct pf_state *s, u_int
>>> flags)
>>> K>  	PF_HASHROW_UNLOCK(ih);
>>> K>  
>>> K>  	pf_detach_state(s);
>>> K> -	refcount_release(&s->refs);
>>> K> +	last = refcount_release(&s->refs);
>>> K> +	KASSERT(last == 0, ("Incorrect state reference count"));
>>> K>  
>>> K>  	return (pf_release_state(s));
>>> K>  }
>>>
>>> IMHO, we shouldn't emit extra code to please Coverity. We can mark 
>>> it
>>> as a false positive in the interface. It may make sense to add a
>>> comment
>>> for a human to explain why return isn't checked here.
>>>
>>
>> Not to mention that when KASSERT compiles to nothing, what you're 
>> left
>> with is a "defined but not used" warning for 'last'.
>>
> I’d really like to keep the KASSERT(), because this is the sort of 
> thing that could go wrong, and the assertion would be helpful.
>
> I suppose I could wrap last in #ifdef INVARIANTS, but that’s rather 
> ugly too.
>
> Asserting that the refcount is at least 1 when entering 
> pf_release_state() would express the same, but that’s also 
> problematic.
> Of course, errors should trigger the KASSERT() in refcount_release(), 
> so I think I may have convinced myself that the KASSERT() can in fact 
> be removed and replaced with (void)refcount_release() and a comment 
> explaining why this refcount_release() can never return 1.
>
So this:

	diff --git a/sys/netpfil/pf/pf.c b/sys/netpfil/pf/pf.c
	index 55ae1145835..0dbf1fe7f66 100644
	--- a/sys/netpfil/pf/pf.c
	+++ b/sys/netpfil/pf/pf.c
	@@ -1623,7 +1623,6 @@ int
	 pf_unlink_state(struct pf_state *s, u_int flags)
	 {
	        struct pf_idhash *ih = &V_pf_idhash[PF_IDHASH(s)];
	-       int last;

	        if ((flags & PF_ENTER_LOCKED) == 0)
	                PF_HASHROW_LOCK(ih);
	@@ -1664,8 +1663,9 @@ pf_unlink_state(struct pf_state *s, u_int flags)
	        PF_HASHROW_UNLOCK(ih);

	        pf_detach_state(s);
	-       last = refcount_release(&s->refs);
	-       KASSERT(last == 0, ("Incorrect state reference count"));
	+       /* pf_state_insert() initialises refs to 2, so we can never 
release the
	+        * last reference here, only in pf_release_state(). */
	+       (void)refcount_release(&s->refs);

	        return (pf_release_state(s));
	 }

I do assume that (void) will tell Coverity I’m deliberately ignoring 
the return value. It’s a fairly common idiom, so I’d expect it to 
understand.

Regards,
Kristof