Subject: Re: Use after free in __dst_destroy_metrics_generic

From: Stefano Brivio <[email-masked]>
Date: Fri, 8 Sep 2017 18:17:00 +0200

On Fri, 8 Sep 2017 09:12:09 -0700
Cong Wang <[email-masked]> wrote:

> On Thu, Sep 7, 2017 at 5:56 PM, Stefano Brivio <[email-masked]> wrote:
> > On Thu, 07 Sep 2017 18:52:02 -0600
> > Subash Abhinov Kasiviswanathan <[email-masked]> wrote:
> >  
> >> We are seeing a possible use after free in ip6_dst_destroy.
> >>
> >> It appears as if memory of the __DST_METRICS_PTR(old) was freed in some
> >> path and allocated
> >> to ion driver. ion driver has also freed it. Finally the memory is freed
> >> by the
> >> fib gc and crashes since it is already deallocated.
> >>
> >> Target is running an ARM64 Android based 4.9 kernel.
> >> Issue was seen once on a regression rack (sorry, no reproducer).
> >> Any pointers to debug this is highly appreciated.
> >>
> >> [ 3489.470581] [<ffffff83c0a289c0>] object_err+0x4c/0x5c
> >> [ 3489.470586] [<ffffff83c0a2b284>] free_debug_processing+0x2e0/0x398
> >> [ 3489.470589] [<ffffff83c0a2b63c>] __slab_free+0x300/0x3e0
> >> [ 3489.470593] [<ffffff83c0a2bfc8>] kfree+0x28c/0x290
> >> [ 3489.470601] [<ffffff83c16b9580>]
> >> __dst_destroy_metrics_generic+0x6c/0x78
> >> [ 3489.470609] [<ffffff83c17d3408>] ip6_dst_destroy+0xb0/0xb4  
> >
> > Should be fixed by:
> >
> > commit ad65a2f05695aced349e308193c6e2a6b1d87112
> > Author: Wei Wang <[email-masked]>
> > Date:   Sat Jun 17 10:42:35 2017 -0700
> >
> >     ipv6: call dst_hold_safe() properly  
> 
> Obviously it should not. One is dst metric, the other is dst.

And obviously you're right. Sorry for the confusion, I blatantly
misread the backtrace.