Re: Use after free in __dst_destroy_metrics_generic

On Fri, 8 Sep 2017 09:12:09 -0700
Cong Wang [off-list ref] wrote:

On Thu, Sep 7, 2017 at 5:56 PM, Stefano Brivio [off-list ref] wrote:

quoted

On Thu, 07 Sep 2017 18:52:02 -0600
Subash Abhinov Kasiviswanathan [off-list ref] wrote:
 

quoted

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 [off-list ref]
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.