Re: ifnet use after free

I'll take a look. But it's likely to not be the OP's issue. For future
reference memguard on the memory type in question is extremely useful in
catching use after free.

-M

On Sat, Aug 25, 2018 at 05:51 Kristof Provost <kp_at_freebsd.org> wrote:

> On 25 Aug 2018, at 0:47, Kristof Provost wrote:
>
> On 25 Aug 2018, at 0:26, Matthew Macy wrote:
>
> On Fri, Aug 24, 2018 at 15:25 Shawn Webb <shawn.webb_at_hardenedbsd.org>
> wrote:
>
> Hey All,
>
> Somewhere in the last month or so, a use after free was introduced. I
> don't have the time right now to bisect the commits and figure out
> which commit introduced the breakage. Attached is the core.txt (which
> seems nonsensical because the dump is reporting on a different
> thread). If the core.txt gets scrubbed, I've posted it here:
> https://gist.github.com/796ea88cec19a1fd2a85f4913482286a
>
> Do you have any guidance on how to reproduce? The hardenedbsd rev isn’t
> useful - the svn commit that it’s based against is what is needed.
>
> For what it’s worth, it’s not a hardenedbsd thing. I’ve been chasing the
> same one (same offset, same allocation size, same most recent user).
> Something gets set to zero/NULL. 8 bytes on amd64, so presumably a pointer.
>
> I currently only trigger it on a development branch, but I’ll see if I can
> clean that up into something I can share tomorrow.
>
> In my test scenario it happens after shutdown of a vnet jail with a few
> interfaces in it (including a pfsync interface which will disappear with
> the jail), and new jails are started. It’s pretty reliable.
>
> At a guess something’s wrong with the delayed cleanup of ifnets and vnet
> shutdown.
>
> I see this:
>
> Memory modified after free 0xfffff800623ab000(2040) val=0 _at_ 0xfffff800623ab398
> panic: Most recently used by ifnet
>
> cpuid = 7
> time = 1535199812
> KDB: stack backtrace:
> db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe008c8e13c0
> vpanic() at vpanic+0x1a3/frame 0xfffffe008c8e1420
> panic() at panic+0x43/frame 0xfffffe008c8e1480
> mtrash_ctor() at mtrash_ctor+0x81/frame 0xfffffe008c8e14a0
> uma_zalloc_arg() at uma_zalloc_arg+0x72c/frame 0xfffffe008c8e1510
> malloc() at malloc+0x9a/frame 0xfffffe008c8e1560
> if_alloc() at if_alloc+0x23/frame 0xfffffe008c8e1590
> epair_clone_create() at epair_clone_create+0x239/frame 0xfffffe008c8e1610
> if_clone_createif() at if_clone_createif+0x4a/frame 0xfffffe008c8e1660
> ifioctl() at ifioctl+0x852/frame 0xfffffe008c8e1750
> kern_ioctl() at kern_ioctl+0x2ba/frame 0xfffffe008c8e17b0
> sys_ioctl() at sys_ioctl+0x15e/frame 0xfffffe008c8e1880
> amd64_syscall() at amd64_syscall+0x28c/frame 0xfffffe008c8e19b0
> fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe008c8e19b0
> --- syscall (54, FreeBSD ELF64, sys_ioctl), rip = 0x80047b74a, rsp = 0x7fffffffe208, rbp = 0x7fffffffe250 ---
> KDB: enter: panic
> [ thread pid 1426 tid 100466 ]
> Stopped at      kdb_enter+0x3b: movq    $0,kdb_why
> db>
>
> It does require a couple of bug fixes in pfsync to trigger. You can get
> them from the pfsync_vnet branch in
> https://github.com/kprovost/freebsd/tree/pfsync_vnet
>
> After that:
> kldload pfsync
> pkg install scapy
> cd /usr/tests/sys/netpfil/pf
> kyua test
>
> It should panic reliably.
>
> Regards,
> Kristof
>