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.w...@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 @
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
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