binder stress testing

Dmitry Vyukov dvyukov at google.com
Sat May 18 07:25:39 UTC 2019


On Fri, May 17, 2019 at 8:34 PM Todd Kjos <tkjos at google.com> wrote:
> > On Fri, May 17, 2019 at 5:51 PM Dmitry Vyukov <dvyukov at google.com> wrote:
> > > > > >
> > > > > > From: Dmitry Vyukov <dvyukov at google.com>
> > > > > > Date: Fri, May 17, 2019 at 3:26 AM
> > > > > > To: Greg Kroah-Hartman, Arve Hjønnevåg, Todd Kjos, Martijn Coenen,
> > > > > > Joel Fernandes, Christian Brauner, open list:ANDROID DRIVERS, LKML
> > > > > > Cc: syzkaller
> > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > I have 2 questions re drivers/android/binder.c stress testing.
> > > > > > >
> > > > > > > 1. Are there any docs on the kernel interface? Or some examples on how
> > > > > > > to use it and reference syscall sequences to make it do something
> > > > > > > meaningful?
> > > > > > > I hopefully figured out struct layouts and offsets of objects thing,
> > > > > > > but I still can't figure out handles, pointers, nodes, pointer to
> > > > > > > nodes... pointer to data (?), references, cookies and where does one
> > > > > > > get valid values for these.
> > > > > >
> > > > > > The kernel interface is not well documented since it isn't intended to
> > > > > > be used apart from libbinder. The best example for your purposes is
> > > > > > probably the binderDriverInterfaceTest which you can find at
> > > > > > https://android.googlesource.com/platform/frameworks/native/+/refs/heads/master/libs/binder/tests/binderDriverInterfaceTest.cpp.
> > > > > >
> > > > > > The libbinder source is at
> > > > > > https://android.googlesource.com/platform/frameworks/native/+/refs/heads/master/libs/binder.
> > > > > >
> > > > > > >
> > > > > > > 2. In my tests any transaction breaks binder device until the next reboot.
> > > > > > > If I open binder device twice, mmap, set context and then the process
> > > > > > > dies, then everything it released fine, in particular the context
> > > > > > > (context_mgr_node gone). So the device is ready for a next test:
> > > > > > >
> > > > > > > [   40.247970][ T6239] binder: binder_open: 6238:6239
> > > > > > > [   40.250819][ T6239] binder: 6238:6239 node 1 u0000000000000000
> > > > > > > c0000000000000000 created
> > > > > > > [   40.253365][ T6239] binder: binder_mmap: 6238 200a0000-200a2000 (8
> > > > > > > K) vma f9 pagep 8000000000000025
> > > > > > > [   40.256454][ T6239] binder: binder_open: 6238:6239
> > > > > > > [   40.259604][ T6239] binder: binder_mmap: 6238 200c0000-200c2000 (8
> > > > > > > K) vma f9 pagep 8000000000000025
> > > > > > > [   40.271526][ T6238] binder: 6238 close vm area 200a0000-200a2000 (8
> > > > > > > K) vma 180200d9 pagep 8000000000000025
> > > > > > > [   40.273113][ T6238] binder: 6238 close vm area 200c0000-200c2000 (8
> > > > > > > K) vma 180200d9 pagep 8000000000000025
> > > > > > > [   40.275058][   T17] binder: binder_flush: 6238 woke 0 threads
> > > > > > > [   40.275997][   T17] binder: binder_flush: 6238 woke 0 threads
> > > > > > > [   40.276968][   T17] binder: binder_deferred_release: 6238 threads
> > > > > > > 0, nodes 0 (ref 0), refs 0, active transactions 0
> > > > > > > [   40.278626][   T17] binder: binder_deferred_release: 6238
> > > > > > > context_mgr_node gone
> > > > > > > [   40.279756][   T17] binder: binder_deferred_release: 6238 threads
> > > > > > > 1, nodes 1 (ref 0), refs 0, active transactions 0
> > > > > > >
> > > > > > >
> > > > > > > However, if I also send a transaction between these fd's, then
> > > > > > > context_mgr_node is not released:
> > > > > > >
> > > > > > > [  783.851403][ T6167] binder: binder_open: 6166:6167
> > > > > > > [  783.858801][ T6167] binder: 6166:6167 node 1 u0000000000000000
> > > > > > > c0000000000000000 created
> > > > > > > [  783.862458][ T6167] binder: binder_mmap: 6166 200a0000-200a2000 (8
> > > > > > > K) vma f9 pagep 8000000000000025
> > > > > > > [  783.865777][ T6167] binder: binder_open: 6166:6167
> > > > > > > [  783.867892][ T6167] binder: binder_mmap: 6166 200c0000-200c2000 (8
> > > > > > > K) vma f9 pagep 8000000000000025
> > > > > > > [  783.870810][ T6167] binder: 6166:6167 write 76 at 0000000020000180,
> > > > > > > read 0 at 0000000020000300
> > > > > > > [  783.872211][ T6167] binder: 6166:6167 BC_TRANSACTION 2 -> 6166 -
> > > > > > > node 1, data 0000000020000200-00000000200002c0 size 88-24-16
> > > > > > > [  783.873819][ T6167] binder: 6166:6167 node 3 u0000000000000000
> > > > > > > c0000000000000000 created
> > > > > > > [  783.875032][ T6167] binder: 6166 new ref 4 desc 1 for node 3
> > > > > > > [  783.875860][ T6167] binder:         node 3 u0000000000000000 -> ref 4 desc 1
> > > > > > > [  783.876868][ T6167] binder: 6166:6167 wrote 76 of 76, read return 0 of 0
> > > > > > > [  783.886714][ T6167] binder: 6166 close vm area 200a0000-200a2000 (8
> > > > > > > K) vma 180200d9 pagep 8000000000000025
> > > > > > > [  783.888161][ T6167] binder: 6166 close vm area 200c0000-200c2000 (8
> > > > > > > K) vma 180200d9 pagep 8000000000000025
> > > > > > > [  783.890134][   T27] binder: binder_flush: 6166 woke 0 threads
> > > > > > > [  783.891036][   T27] binder: binder_flush: 6166 woke 0 threads
> > > > > > > [  783.892027][ T2903] binder: release 6166:6167 transaction 2 out, still active
> > > > > > > [  783.893097][ T2903] binder: unexpected work type, 4, not freed
> > > > > > > [  783.893947][ T2903] binder: undelivered TRANSACTION_COMPLETE
> > > > > > > [  783.894849][ T2903] binder: node 3 now dead, refs 1, death 0
> > > > > > > [  783.895717][ T2903] binder: binder_deferred_release: 6166 threads
> > > > > > > 1, nodes 1 (ref 1), refs 0, active transactions 1
> > > > > > >
> > > > > > >
> > > > > > > And all subsequent tests will fail because "BINDER_SET_CONTEXT_MGR
> > > > > > > already set" presumably to the now unrecoverably dead process:
> > > > > > >
> > > > > > > [  831.085174][ T6191] binder: binder_open: 6190:6191
> > > > > > > [  831.087450][ T6191] binder: BINDER_SET_CONTEXT_MGR already set
> > > > > > > [  831.088910][ T6191] binder: 6190:6191 ioctl 4018620d 200000c0 returned -16
> > > > > > > [  831.090626][ T6191] binder: binder_mmap: 6190 200a0000-200a2000 (8
> > > > > > > K) vma f9 pagep 8000000000000025
> > > > > > > [  831.092783][ T6191] binder: binder_open: 6190:6191
> > > > > > > [  831.094076][ T6191] binder: binder_mmap: 6190 200c0000-200c2000 (8
> > > > > > > K) vma f9 pagep 8000000000000025
> > > > > > > [  831.096218][ T6191] binder: 6190:6191 write 76 at 0000000020000180,
> > > > > > > read 0 at 0000000020000300
> > > > > > > [  831.097606][ T6191] binder: 6190:6191 BC_TRANSACTION 5 -> 6166 -
> > > > > > > node 1, data 0000000020000200-00000000200002c0 size 88-24-16
> > > > > > > [  831.099251][ T6191] binder_alloc: 6166: binder_alloc_buf, no vma
> > > > > > > [  831.100433][ T6191] binder: 6190:6191 transaction failed 29189/-3,
> > > > > > > size 88-24 line 3157
> > > > > > > [  831.101559][ T6191] binder: 6190:6191 wrote 76 of 76, read return 0 of 0
> > > > > > > [  831.110317][ T6191] binder: 6190 close vm area 200a0000-200a2000 (8
> > > > > > > K) vma 180200d9 pagep 8000000000000025
> > > > > > > [  831.111752][ T6191] binder: 6190 close vm area 200c0000-200c2000 (8
> > > > > > > K) vma 180200d9 pagep 8000000000000025
> > > > > > > [  831.113266][ T3344] binder: binder_flush: 6190 woke 0 threads
> > > > > > > [  831.114147][ T3344] binder: binder_flush: 6190 woke 0 threads
> > > > > > > [  831.115087][ T3344] binder: undelivered TRANSACTION_ERROR: 29189
> > > > > > > [  831.115991][ T3344] binder: binder_deferred_release: 6190 threads
> > > > > > > 1, nodes 0 (ref 0), refs 0, active transactions 0
> > > > > > > [  831.117525][ T3344] binder: binder_deferred_release: 6190 threads
> > > > > > > 1, nodes 0 (ref 0), refs 0, active transactions 0
> > > > > > >
> > > > > > >
> > > > > > > The question is: if processes that opened the device and ever mapped
> > > > > > > it are now completely gone, should it reset the original state when
> > > > > > > context can be bound again? Is it a bug in binder that it does not? If
> > > > > > > so, is there some kind of temp work-around for this?
> > > > > >
> > > > > > If all the processes that opened the device are gone, everything
> > > > > > should be cleaned up and leave binder in a useable state. When the
> > > > > > device is in this state, can you dump out
> > > > > > /sys/debug/kernel/binder/state and send it to me?
> > > > >
> > > > >
> > > > > Here it is:
> > > > >
> > > > >
> > > > > binder state:
> > > > > dead nodes:
> > > > >   node 3: u0000000000000000 c0000000000000000 hs 0 hw 0 ls 0 lw 0 is 1
> > > > > iw 1 tr 1 proc 6193
> > > > > proc 6193
> > > >
> > > > /\/\/\
> > > >
> > > > This process does not exist anymore for minutes. Like at all. Even no
> > > > procfs node.
> > > >
> > > > > context binder0
> > > > >   thread 6194: l 00 need_return 1 tr 0
> > > > >   node 1: u0000000000000000 c0000000000000000 hs 1 hw 1 ls 2 lw 1 is 0 iw 0 tr 1
> > > > >   ref 4: desc 1 dead node 3 s 1 w 0 d 00000000e77aea3b
> > > > >   buffer 2: 00000000b2301cfa size 88:24:16 active
> > > > >   pending transaction 2: 00000000b1591166 from 0:0 to 6193:0 code 0
> > > > > flags 0 pri 0 r1 node 1 size 88:24 data 00000000b2301cfa
> > > > >
> > > > >
> > > > >
> > > > > Kernel also said:
> > > > >
> > > > > [  197.049702][   T12] binder: release 6193:6194 transaction 2 out, still active
> > > > > [  197.050803][   T12] binder: unexpected work type, 4, not freed
> > > > > [  197.051658][   T12] binder: undelivered TRANSACTION_COMPLETE
> > > > >
> > > > > Not sure why there is something unexpected. I don't try to fuzz it or
> > > > > something at this point. Just run a basic test.
> > > > > Here is the test, it's in syzkaller notation, but hopefully you can
> > > > > get overall idea:
> > > > >
> > > > > r0 = syz_open_dev$binder(&AUTO='/dev/binder#\x00', 0x0, 0x2)
> > > > > ioctl$BINDER_SET_CONTEXT_MGR_EXT(r0, AUTO, &AUTO={AUTO, 0x100, 0x0, 0x0})
> > > > > mmap$binder(&(0x7f00000a0000), 0x2000, 0x1, 0x11, r0, 0x0)
> > > > > r1 = syz_open_dev$binder(&AUTO='/dev/binder#\x00', 0x0, 0x2)
> > > > > mmap$binder(&(0x7f00000c0000), 0x2000, 0x1, 0x11, r1, 0x0)
> > > > > ioctl$BINDER_WRITE_READ(r1, AUTO, &AUTO={AUTO, AUTO,
> > > > > &AUTO=[@transaction_sg={AUTO, {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
> > > > > AUTO, AUTO, &AUTO={@flat=@binder={AUTO, 0x0, 0x0, 0x0}, @fd={AUTO,
> > > > > AUTO, r0, AUTO, 0x0}, @ptr={AUTO, 0x0, &AUTO=""/10, AUTO, 0x0, 0x0}},
> > > > > &AUTO={AUTO, AUTO, AUTO}}, 0x10}], AUTO, AUTO, &AUTO})
> > >
> > >
> > > Here is corresponding C test that you can use:
> > > https://gist.githubusercontent.com/dvyukov/484368950289954516e352a0d086794b/raw/fab6b0fb3ef7af57c3040a3adeed26bcf03e75a6/gistfile1.txt
> >
> > Wait, is it because I send binder fd in BINDER_TYPE_FD object?
> > I was just testing different object types and for BINDER_TYPE_FD I
> > needed an fd, and the binder fd was the only fd that the test already
> > had opened, so I was like OK, here is an fd if you need one here....
> > Can it be a problem in real life? But either way this deadlock is
> > quite unpleasant for fuzzing...
>
> Which kernel branch is this? I think you are seeing an issue that
> should have been fixed in mainline by 7aa135fcf263 ("ANDROID: binder:
> prevent transactions into own process."). The process is sending a
> transaction to itself which should have failed.
>
> The hang is because the handling of BINDER_TYPE_FD does an fget() on
> the fd (which is on /dev/binder0 in this case). Since the transaction
> is stuck on the queue (no server thread to handle it), no one is
> calling fput(). The result is that exit() doesn't result in
> binder_release() being called to cleanup the process binder state.
>
> So, if you use a different fd, the issue would be avoided -- but as I
> said, this shouldn't have happened in the first place on mainline, so
> if this is mainline or any branch that has the above patch, there is a
> new driver bug that is somehow allowing transactions to self.

I am on the latest Linus tree:

commit 63863ee8e2f6f6ae47be3dff4af2f2806f5ca2dd (HEAD -> master,
origin/master, origin/HEAD)
Merge: fbcde197e1be 259799ea5a9a
Author: Linus Torvalds <torvalds at linux-foundation.org>
Date:   Mon May 13 16:01:52 2019 -0700

The commit you mentioned is already there. You can check the C repro
how it sends such a transaction.


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