D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

This revision was automatically updated to reflect the committed changes.
Closed by commit R320:94e7b64325f9: [KIO-MTP] Fix null pointer dereference 
(authored by feverfew).

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AFFECTED FILES
  mtp/kiod_module/mtpdevice.cpp

To: feverfew, akrutzler, dfaure, elvisangelaccio
Cc: anthonyfieroni, kde-frameworks-devel, fvogt, kfm-devel, ngraham, azyx, 
nikolaik, pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, rdieter, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Elvis Angelaccio]

elvisangelaccio added a comment.


  In D28535#642298 , @feverfew wrote:
  
  > In D28535#642289 , 
@elvisangelaccio wrote:
  >
  > > In D28535#640833 , @fvogt 
wrote:
  > >
  > > > I assume there is a reason why `MTPDevice::getDevice()` has code for 
handling this very specific case, so I wouldn't just remove it without figuring 
out why: https://i.redd.it/hfnl7xo8yovy.gif
  > > >
  > > > If not, that would indeed be the best option.
  > >
  > >
  > > Unfortunately git blame doesn't seem to help us here.
  > >
  > > I suggest to push this fix to master only and see what happens.
  >
  >
  > By pushing this to master would we still be able to throw it up to 20.04.* 
if we decide it's stable enough? (also need to know to know what to put down as 
the FIXED-IN in the commit message)?
  
  
  Sure, we can cherry-pick that commit later.

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To: feverfew, akrutzler, dfaure, elvisangelaccio
Cc: anthonyfieroni, kde-frameworks-devel, fvogt, kfm-devel, ngraham, azyx, 
nikolaik, pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, rdieter, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew added a comment.


  In D28535#642298 , @feverfew wrote:
  
  > In D28535#642289 , 
@elvisangelaccio wrote:
  >
  > > In D28535#640833 , @fvogt 
wrote:
  > >
  > > > I assume there is a reason why `MTPDevice::getDevice()` has code for 
handling this very specific case, so I wouldn't just remove it without figuring 
out why: https://i.redd.it/hfnl7xo8yovy.gif
  > > >
  > > > If not, that would indeed be the best option.
  > >
  > >
  > > Unfortunately git blame doesn't seem to help us here.
  > >
  > > I suggest to push this fix to master only and see what happens.
  >
  >
  > By pushing this to master would we still be able to throw it up to 20.04.* 
if we decide it's stable enough? (also need to know to know what to put down as 
the FIXED-IN in the commit message)?
  
  
  @elvisangelaccio ping seeming as 20.04 release is close...

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To: feverfew, akrutzler, dfaure, elvisangelaccio
Cc: anthonyfieroni, kde-frameworks-devel, fvogt, kfm-devel, ngraham, azyx, 
nikolaik, pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, rdieter, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew added a comment.


  In D28535#642289 , 
@elvisangelaccio wrote:
  
  > In D28535#640833 , @fvogt wrote:
  >
  > > I assume there is a reason why `MTPDevice::getDevice()` has code for 
handling this very specific case, so I wouldn't just remove it without figuring 
out why: https://i.redd.it/hfnl7xo8yovy.gif
  > >
  > > If not, that would indeed be the best option.
  >
  >
  > Unfortunately git blame doesn't seem to help us here.
  >
  > I suggest to push this fix to master only and see what happens.
  
  
  By pushing this to master would we still be able to throw it up to 20.04.* if 
we decide it's stable enough?

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Cc: anthonyfieroni, kde-frameworks-devel, fvogt, kfm-devel, ngraham, nikolaik, 
pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, rdieter, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  @elvisangelaccio this peace of code is purely wrong at least `m_storages` is 
not updated to new device and not only. This code should never exists or try to 
hide some other bug.

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pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, rdieter, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Elvis Angelaccio]

elvisangelaccio accepted this revision.
elvisangelaccio added a comment.
This revision is now accepted and ready to land.


  In D28535#640833 , @fvogt wrote:
  
  > I assume there is a reason why `MTPDevice::getDevice()` has code for 
handling this very specific case, so I wouldn't just remove it without figuring 
out why: https://i.redd.it/hfnl7xo8yovy.gif
  >
  > If not, that would indeed be the best option.
  
  
  Unfortunately git blame doesn't seem to help us here.
  
  I suggest to push this fix to master only and see what happens.

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pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, rdieter, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  Ok that's look good to me. We can move that code in constructor just before 
loop for storages, then use m_mtpdevice instead of raw device, but it looks 
like removed code is just a noise and it shouldn't present at all.
  
  +1

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pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
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D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew added a comment.


  Ok so I've updated the code as can be seen. Mucked around with 
disconnecting/connecting, no issues on my side at least.

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Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
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D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew updated this revision to Diff 79252.
feverfew added a comment.


  - Don't try to release device in get method

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AFFECTED FILES
  mtp/kiod_module/mtpdevice.cpp

To: feverfew, akrutzler, dfaure, elvisangelaccio
Cc: anthonyfieroni, kde-frameworks-devel, fvogt, kfm-devel, ngraham, nikolaik, 
pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Fabian Vogt]

fvogt added a comment.


  I assume there is a reason why `MTPDevice::getDevice()` has code for handling 
this very specific case, so I wouldn't just remove it without figuring out why: 
../https://i.redd.it/hfnl7xo8yovy.gif
  
  If not, that would indeed be the best option.

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pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew added a comment.


  In D28535#640703 , @anthonyfieroni 
wrote:
  
  > In D28535#640699 , @feverfew 
wrote:
  >
  > > So to be succinct, the only correct fix here is to change `getDevice()` 
to `return m_mtpdevice`?
  >
  >
  > Yes, then check if it's crash, in all other places `LIBMTP_xxx` should take 
care of and return false or nullptr depend of function returning value.
  
  
  What do you mean by "then check if it's crash"? Surely we should do nothing 
and let LIBMTP sort out printing errors and stuff? Eventually the device should 
be reclaimed by the daemon anyway via the help of `Solid::deviceRemoved()`. I 
agree with everything after the comma though, `LIBMTP_mtpdevice_t *` should 
never be freed unless we explicitly do so ourselves.

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Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  In D28535#640699 , @feverfew wrote:
  
  > So to be succinct, the only correct fix here is to change `getDevice()` to 
`return m_mtpdevice`?
  
  
  Yes, then check if it's crash, in all other place `LIBMTP_xxx` should take 
care of and return false or nullptr depend of function returning value.

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pberestov, iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, 
Codezela, feverfew, meven, michaelh, spoorun, navarromorales, firef, 
andrebarros, bruns, emmanuelp, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew added a comment.


  If you want to, feel free, I'm a bit tight on time. But I will say this. the 
whole `getDevice()` function confuses me. I'm not entirely sure why this `if` 
check is necessary at all. The lifetime of devices and its children (i.e 
storage) should be managed by the KMTPD daemon AFAICT. A device shouldn't be 
trying to re-open itself anywhere IMO. To me the getDevice() function should 
simply be a simple return to avoid this NULL issue happening. Even if a device 
doesn't exist anymore, no segfaults should happen when passing an "invalid" 
`LIBMTP_device_T` to any other `LIBMTP` function?
  
  So to be succinct, the only correct fix here is to change `getDevice()` to 
`return m_mtpdevice`?

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D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  @feverfew are you gonna try what i'm writing about or i should do it? Just 
use cached device, do not reopen since it'll return nullptr.

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D28535: [KIO-MTP] Fix null pointer dereference

[Fabian Vogt]

fvogt added a comment.


  In D28535#640682 , @feverfew wrote:
  
  > In D28535#640674 , @fvogt wrote:
  >
  > > What you're suggesting is to change `MTPDevice::getDevice` to return the 
old device if reopening fails - but reopening without releasing might not work.
  >
  >
  > This seems to be a robust solution IMO, why do you suspect this might not 
work?
  
  
  Because there can only be a single libusb session per device. So you have to 
release the old one before opening again.

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D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew added a comment.


  In D28535#640674 , @fvogt wrote:
  
  > What you're suggesting is to change `MTPDevice::getDevice` to return the 
old device if reopening fails - but reopening without releasing might not work.
  
  
  This seems to be a robust solution IMO, why do you suspect this might not 
work?

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andrebarros, bruns, emmanuelp, mikesomov

D28535: [KIO-MTP] Fix null pointer dereference

[Fabian Vogt]

fvogt added a comment.


  In D28535#640680 , @anthonyfieroni 
wrote:
  
  > I see we don't speak in same language :)
  >  `LIBMTP_Open_Raw_Device_Uncached(_rawdevice);`
  >  returns nullptr that's normal since device is inaccessible, i mean it does 
not need to call `LIBMTP_Release_Device` using `m_mtpdevice` is safe it's not 
nullptr, it's just a disconnected device and libmtp knows that.
  
  
  Yes, and until that point everything is fine.
  Only after `m_mtpdevice = LIBMTP_Open_Raw_Device_Uncached(_rawdevice);`, 
which sets `m_mtpdevice` to nullptr it goes down the path I outlined.

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D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  I see we don't speak in same language :)
  `LIBMTP_Open_Raw_Device_Uncached(_rawdevice);`
  returns nullptr that's normal since device is inaccessible, i mean it does 
not need to call `LIBMTP_Release_Device` using `m_mtpdevice` is safe it's not 
nullptr, it's just a disconnected device and libmtp knows that.

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D28535: [KIO-MTP] Fix null pointer dereference

[Fabian Vogt]

fvogt added a comment.


  There is no such thing as an "invalid device" at that point anymore. There's 
only nullptr.
  
LIBMTP_mtpdevice_t *MTPDevice::getDevice()
{
if (!m_mtpdevice->storage) {
qCDebug(LOG_KIOD_KMTPD) << "no storage found: reopen mtpdevice";
LIBMTP_Release_Device(m_mtpdevice);
m_mtpdevice = LIBMTP_Open_Raw_Device_Uncached(_rawdevice);
}

return m_mtpdevice;
}
  
  What you're suggesting is to change `MTPDevice::getDevice` to return the old 
device if reopening fails - but reopening without releasing might not work.

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D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  In D28535#640672 , @fvogt wrote:
  
  > If `getDevice()` returns nullptr, this means that `MTPDevice::getDevice()` 
returns nullptr. This can only happen if `m_mtpdevice` is nullptr, which will 
crash in `MTPDevice::~MTPDevice` sooner or later anyway.
  
  
  I don't think so, libmtp knows device is not available then 
`LIBMTP_Release_Device` (invalid device) will not crash. So i prefer to cache 
device in storage as well so libmtp will just return false on invalid device.

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D28535: [KIO-MTP] Fix null pointer dereference

[Fabian Vogt]

fvogt added a comment.


  In D28535#640656 , @anthonyfieroni 
wrote:
  
  > You're right about bug report, but it can fail in any other place, just in 
particular version it happen in  `updateStorageInfo` Can we cache `getDevice` 
in m_device (in constructor) then use it everywhere. I think libmtp has guard 
against disconnected device and will not crash.
  
  
  `MTPDevice` already does that.
  
  If `getDevice()` returns nullptr, this means that `MTPDevice::getDevice()` 
returns nullptr. This can only happen if `m_mtpdevice` is nullptr, which will 
crash in `MTPDevice::~MTPDevice` sooner or later anyway.
  
  So this patch will at most just delay the crash.
  
  AFAICT `MTPDevice` is supposed to be destroyed in `KMTPd::deviceRemoved` on 
disconnection, but this is obviously racy.

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D28535: [KIO-MTP] Fix null pointer dereference

[Anthony Fieroni]

anthonyfieroni added a comment.


  You're right about bug report, but it can fail in any other place, just in 
particular version it happen in  `updateStorageInfo` Can we cache `getDevice` 
in m_device (in constructor) then use it everywhere. I think libmtp has guard 
against disconnected device and will not crash.

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D28535: [KIO-MTP] Fix null pointer dereference

[Alexander Saoutkin]

feverfew created this revision.
feverfew added reviewers: akrutzler, dfaure, elvisangelaccio.
Herald added projects: Dolphin, Frameworks.
Herald added subscribers: kfm-devel, kde-frameworks-devel.
feverfew requested review of this revision.

REVISION SUMMARY
  A null pointer can be returned from getDevice() if a device is disconnected.
  Passing NULL into LIBMTP_Get_Storage() results in a NULL pointer dereference.
  
  BUG: 405838

TEST PLAN
  Compiles. I couldn't reproduce this as described in the bug report, but from
  reading the attached stacktrace in the bug report it's obvious what went wrong
  here.

REPOSITORY
  R320 KIO Extras

BRANCH
  fixNullPtr (branched from master)

REVISION DETAIL
  https://phabricator.kde.org/D28535

AFFECTED FILES
  mtp/kiod_module/mtpstorage.cpp

To: feverfew, akrutzler, dfaure, elvisangelaccio
Cc: kde-frameworks-devel, fvogt, kfm-devel, ngraham, nikolaik, pberestov, 
iasensio, fprice, LeGast00n, cblack, fbampaloukas, alexde, GB_2, Codezela, 
feverfew, meven, michaelh, spoorun, navarromorales, firef, andrebarros, bruns, 
emmanuelp, mikesomov