[PATCH] ifaddr leak when modifying a route

[Ryan Stone]

I've put this phab review up that patches an ifaddr refcount leak in
the routing code.  When a route is modified in a way that modifies
rt->rt_ifa, in most cases we don't release the reference on the old
one, which can cause it to leak.  I have a simple script here that I
wrote to demonstrate the issue:

https://people.freebsd.org/~rstone/route-change-leak

If I run it on a stock -head system, I see 100 ifaddrs leak every time it's run:

# sh route-change-leak
         Type InUse MemUse HighUse Requests  Size(s)
       ifaddr    53    17K       -      564  32,64,128,256,512,2048,4096
       ifaddr   153    42K       -      664  32,64,128,256,512,2048,4096
# sh route-change-leak
         Type InUse MemUse HighUse Requests  Size(s)
       ifaddr   153    42K       -      665  32,64,128,256,512,2048,4096
       ifaddr   253    67K       -      765  32,64,128,256,512,2048,4096
# sh route-change-leak
         Type InUse MemUse HighUse Requests  Size(s)
       ifaddr   253    67K       -      766  32,64,128,256,512,2048,4096
       ifaddr   353    92K       -      866  32,64,128,256,512,2048,4096

With my fix, the leak is gone:

# sh route-change-leak
         Type InUse MemUse HighUse Requests  Size(s)
       ifaddr    46    15K       -       47  16,32,64,128,256,512,2048,4096
       ifaddr    46    15K       -      147  16,32,64,128,256,512,2048,4096
# sh route-change-leak
         Type InUse MemUse HighUse Requests  Size(s)
       ifaddr    46    15K       -      148  16,32,64,128,256,512,2048,4096
       ifaddr    46    15K       -      248  16,32,64,128,256,512,2048,4096

The review is here.  I didn't subscribe freebsd-net to the review to
try to reduce the noise on the mailing list, so if you would like to
review this change please subscribe yourself to the review.  Thanks.

https://reviews.freebsd.org/D13417