linux.git/drivers/comedi/comedi_fops.c, branch v6.17

comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()

2025-08-19T10:56:47+00:00

syzbot reports a KMSAN kernel-infoleak in `do_insn_ioctl()`.  A kernel
buffer is allocated to hold `insn->n` samples (each of which is an
`unsigned int`).  For some instruction types, `insn->n` samples are
copied back to user-space, unless an error code is being returned.  The
problem is that not all the instruction handlers that need to return
data to userspace fill in the whole `insn->n` samples, so that there is
an information leak.  There is a similar syzbot report for
`do_insnlist_ioctl()`, although it does not have a reproducer for it at
the time of writing.

One culprit is `insn_rw_emulate_bits()` which is used as the handler for
`INSN_READ` or `INSN_WRITE` instructions for subdevices that do not have
a specific handler for that instruction, but do have an `INSN_BITS`
handler.  For `INSN_READ` it only fills in at most 1 sample, so if
`insn->n` is greater than 1, the remaining `insn->n - 1` samples copied
to userspace will be uninitialized kernel data.

Another culprit is `vm80xx_ai_insn_read()` in the "vm80xx" driver.  It
never returns an error, even if it fails to fill the buffer.

Fix it in `do_insn_ioctl()` and `do_insnlist_ioctl()` by making sure
that uninitialized parts of the allocated buffer are zeroed before
handling each instruction.

Thanks to Arnaud Lecomte for their fix to `do_insn_ioctl()`.  That fix
replaced the call to `kmalloc_array()` with `kcalloc()`, but it is not
always necessary to clear the whole buffer.

Fixes: ed9eccbe8970 ("Staging: add comedi core")
Reported-by: syzbot+a5e45f768aab5892da5d@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a5e45f768aab5892da5d
Reported-by: syzbot+fb4362a104d45ab09cf9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fb4362a104d45ab09cf9
Cc: stable  # 5.13+
Cc: Arnaud Lecomte 
Signed-off-by: Ian Abbott 
Link: https://lore.kernel.org/r/20250725125324.80276-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman

Merge tag 'char-misc-6.17-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc

2025-07-29T16:52:01+00:00

Pull char / misc / IIO / other driver updates from Greg KH:
 "Here is the big set of char/misc/iio and other smaller driver
  subsystems for 6.17-rc1. It's a big set this time around, with the
  huge majority being in the iio subsystem with new drivers and dts
  files being added there.

  Highlights include:
   - IIO driver updates, additions, and changes making more code const
     and cleaning up some init logic
   - bus_type constant conversion changes
   - misc device test functions added
   - rust miscdevice minor fixup
   - unused function removals for some drivers
   - mei driver updates
   - mhi driver updates
   - interconnect driver updates
   - Android binder updates and test infrastructure added
   - small cdx driver updates
   - small comedi fixes
   - small nvmem driver updates
   - small pps driver updates
   - some acrn virt driver fixes for printk messages
   - other small driver updates

  All of these have been in linux-next with no reported issues"

* tag 'char-misc-6.17-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc: (292 commits)
  binder: Use seq_buf in binder_alloc kunit tests
  binder: Add copyright notice to new kunit files
  misc: ti_fpc202: Switch to of_fwnode_handle()
  bus: moxtet: Use dev_fwnode()
  pc104: move PC104 option to drivers/Kconfig
  drivers: virt: acrn: Don't use %pK through printk
  comedi: fix race between polling and detaching
  interconnect: qcom: Add Milos interconnect provider driver
  dt-bindings: interconnect: document the RPMh Network-On-Chip Interconnect in Qualcomm Milos SoC
  mei: more prints with client prefix
  mei: bus: use cldev in prints
  bus: mhi: host: pci_generic: Add Telit FN990B40 modem support
  bus: mhi: host: Detect events pointing to unexpected TREs
  bus: mhi: host: pci_generic: Add Foxconn T99W696 modem
  bus: mhi: host: Use str_true_false() helper
  bus: mhi: host: pci_generic: Add support for EM929x and set MRU to 32768 for better performance.
  bus: mhi: host: Fix endianness of BHI vector table
  bus: mhi: host: pci_generic: Disable runtime PM for QDU100
  bus: mhi: host: pci_generic: Fix the modem name of Foxconn T99W640
  dt-bindings: interconnect: qcom,msm8998-bwmon: Allow 'nonposted-mmio'
  ...

comedi: fix race between polling and detaching

2025-07-22T16:47:30+00:00

syzbot reports a use-after-free in comedi in the below link, which is
due to comedi gladly removing the allocated async area even though poll
requests are still active on the wait_queue_head inside of it. This can
cause a use-after-free when the poll entries are later triggered or
removed, as the memory for the wait_queue_head has been freed.  We need
to check there are no tasks queued on any of the subdevices' wait queues
before allowing the device to be detached by the `COMEDI_DEVCONFIG`
ioctl.

Tasks will read-lock `dev->attach_lock` before adding themselves to the
subdevice wait queue, so fix the problem in the `COMEDI_DEVCONFIG` ioctl
handler by write-locking `dev->attach_lock` before checking that all of
the subdevices are safe to be deleted.  This includes testing for any
sleepers on the subdevices' wait queues.  It remains locked until the
device has been detached.  This requires the `comedi_device_detach()`
function to be refactored slightly, moving the bulk of it into new
function `comedi_device_detach_locked()`.

Note that the refactor of `comedi_device_detach()` results in
`comedi_device_cancel_all()` now being called while `dev->attach_lock`
is write-locked, which wasn't the case previously, but that does not
matter.

Thanks to Jens Axboe for diagnosing the problem and co-developing this
patch.

Cc: stable 
Fixes: 2f3fdcd7ce93 ("staging: comedi: add rw_semaphore to protect against device detachment")
Link: https://lore.kernel.org/all/687bd5fe.a70a0220.693ce.0091.GAE@google.com/
Reported-by: syzbot+01523a0ae5600aef5895@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=01523a0ae5600aef5895
Co-developed-by: Jens Axboe 
Signed-off-by: Jens Axboe 
Signed-off-by: Ian Abbott 
Tested-by: Jens Axboe 
Link: https://lore.kernel.org/r/20250722155316.27432-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman

comedi: Fix initialization of data for instructions that write to subdevice

2025-07-16T13:02:44+00:00

Some Comedi subdevice instruction handlers are known to access
instruction data elements beyond the first `insn->n` elements in some
cases.  The `do_insn_ioctl()` and `do_insnlist_ioctl()` functions
allocate at least `MIN_SAMPLES` (16) data elements to deal with this,
but they do not initialize all of that.  For Comedi instruction codes
that write to the subdevice, the first `insn->n` data elements are
copied from user-space, but the remaining elements are left
uninitialized.  That could be a problem if the subdevice instruction
handler reads the uninitialized data.  Ensure that the first
`MIN_SAMPLES` elements are initialized before calling these instruction
handlers, filling the uncopied elements with 0.  For
`do_insnlist_ioctl()`, the same data buffer elements are used for
handling a list of instructions, so ensure the first `MIN_SAMPLES`
elements are initialized for each instruction that writes to the
subdevice.

Fixes: ed9eccbe8970 ("Staging: add comedi core")
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Ian Abbott 
Link: https://lore.kernel.org/r/20250707161439.88385-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman

comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

2025-07-16T12:58:54+00:00

The handling of the `COMEDI_INSNLIST` ioctl allocates a kernel buffer to
hold the array of `struct comedi_insn`, getting the length from the
`n_insns` member of the `struct comedi_insnlist` supplied by the user.
The allocation will fail with a WARNING and a stack dump if it is too
large.

Avoid that by failing with an `-EINVAL` error if the supplied `n_insns`
value is unreasonable.

Define the limit on the `n_insns` value in the `MAX_INSNS` macro.  Set
this to the same value as `MAX_SAMPLES` (65536), which is the maximum
allowed sum of the values of the member `n` in the array of `struct
comedi_insn`, and sensible comedi instructions will have an `n` of at
least 1.

Reported-by: syzbot+d6995b62e5ac7d79557a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d6995b62e5ac7d79557a
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Tested-by: Ian Abbott 
Cc: stable@vger.kernel.org # 5.13+
Signed-off-by: Ian Abbott 
Link: https://lore.kernel.org/r/20250704120405.83028-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman

comedi: allocate DMA coherent buffer as individual pages

2025-04-25T13:53:19+00:00

Depending on the driver, the acquisition buffer is allocated either from
normal memory, or from DMA coherent memory.  For normal memory, the
buffer is allocated as individual pages, but for DMA coherent memory, it
is allocated as a single block.  Prior to commit e36472145aa7 ("staging:
comedi: use dma_mmap_coherent for DMA-able buffer mmap"), the buffer was
allocated as individual pages for DMA coherent memory too, but that was
changed to allocate it as a single block to allow `dma_mmap_coherent()`
to be used to mmap it, because that requires the pages being mmap'ed to
be contiguous.

This patch allocates the buffer from DMA coherent memory a page at a
time again, and works around the limitation of `dma_mmap_coherent()` by
calling it in a loop for each page, with temporarily modified `vm_start`
and `vm_end` values in the VMA.  (The `vm_pgoff` value is 0.)

Cc: Christoph Hellwig 
Signed-off-by: Ian Abbott 
Link: https://lore.kernel.org/r/20250415114008.5977-5-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman

comedi: access buffer data page-by-page

2025-04-25T13:53:18+00:00

The aim is to get rid of the `prealloc_buf` member of `struct
comedi_async` and access the buffer contents on a page-by-page basis
using the addresses in the `virt_addr` member of `struct
comedi_buf_page`.  This will allow us to eliminate a `vmap()` that maps
the whole buffer.

Since the buffer pages have non-consecutive `virt_addr` addresses in
virtual memory (except for drivers using DMA), change the loops that
access buffer data to access it page-by-page.

Signed-off-by: Ian Abbott 
Link: https://lore.kernel.org/r/20250415114008.5977-3-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman

comedi: Flush partial mappings in error case

2024-11-05T13:01:07+00:00

If some remap_pfn_range() calls succeeded before one failed, we still have
buffer pages mapped into the userspace page tables when we drop the buffer
reference with comedi_buf_map_put(bm). The userspace mappings are only
cleaned up later in the mmap error path.

Fix it by explicitly flushing all mappings in our VMA on the error path.

See commit 79a61cc3fc04 ("mm: avoid leaving partial pfn mappings around in
error case").

Cc: stable@vger.kernel.org
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Signed-off-by: Jann Horn 
Link: https://lore.kernel.org/r/20241017-comedi-tlb-v3-1-16b82f9372ce@google.com
Signed-off-by: Greg Kroah-Hartman

drivers/comedi: use standard array-copy-function

2023-12-07T02:08:45+00:00

comedi_fops.c utilizes memdup_user() to copy a userspace array.

The new function memdup_array_user() provides a standardized way to copy
userspace-arrays. It makes it easier to see that an array is being
copied and, additionally, performs a generic overflow-check which might
help make the code more robust in case of changes in the future.

Replace memdup_user() with memdup_array_user().

Suggested-by: Dave Airlie 
Signed-off-by: Philipp Stanner 
Reviewed-by: Ian Abbott 
Link: https://lore.kernel.org/r/20231103112932.75795-2-pstanner@redhat.com
Signed-off-by: Greg Kroah-Hartman

comedi: make all 'class' structures const

2023-06-23T08:29:02+00:00

Now that the driver core allows for struct class to be in read-only
memory, making all 'class' structures to be declared at build time
placing them into read-only memory, instead of having to be dynamically
allocated at load time.

Cc: Ian Abbott 
Cc: H Hartley Sweeten 
Cc: Benjamin Tissoires 
Cc: Ivan Orlov 
Cc: Xuezhi Zhang 
Suggested-by: Greg Kroah-Hartman 
Signed-off-by: Ivan Orlov 
Link: https://lore.kernel.org/r/20230620144137.581406-2-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman