Date:   Fri, 17 May 2019 11:34:16 -0700
From:   Todd Kjos <tkjos@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: binder stress testing

On Fri, May 17, 2019 at 8:55 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Fri, May 17, 2019 at 5:51 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > > > >
> > > > > From: Dmitry Vyukov <dvyukov@...gle.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={@...t=@...der={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.

-Todd

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