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Ian Abbott 0171980795 comedi: fix race between polling and detaching 
commit 35b6fc51c6 upstream.

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 <stable@kernel.org>
Fixes: 2f3fdcd7ce ("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 <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Tested-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20250722155316.27432-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-08-20 18:30:52 +02:00
arch MIPS: lantiq: falcon: sysctrl: fix request memory check logic 2025-08-20 18:30:43 +02:00
block block: Introduce bio_needs_zone_write_plugging() 2025-08-20 18:30:51 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: jitter - fix intermediary handling 2025-08-20 18:30:42 +02:00
Documentation Documentation: ACPI: Fix parent device references 2025-08-20 18:30:15 +02:00
drivers comedi: fix race between polling and detaching 2025-08-20 18:30:52 +02:00
fs ext4: initialize superblock fields in the kballoc-test.c kunit tests 2025-08-20 18:30:52 +02:00
include block: Introduce bio_needs_zone_write_plugging() 2025-08-20 18:30:51 +02:00
init io_uring: fix breakage in EXPERT menu 2025-08-15 12:13:32 +02:00
io_uring io_uring/poll: fix POLLERR handling 2025-07-24 08:56:23 +02:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel printk: nbcon: Allow reacquire during panic 2025-08-20 18:30:47 +02:00
lib lib/sbitmap: convert shallow_depth from one word to the whole sbitmap 2025-08-20 18:30:49 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/damon/core: commit damos->target_nid 2025-08-20 18:30:51 +02:00
net vsock/virtio: Resize receive buffers so that each SKB fits in a 4K page 2025-08-20 18:30:40 +02:00
rust rust: use #[used(compiler)] to fix build and modpost with Rust >= 1.89.0 2025-07-24 08:56:37 +02:00
samples samples: mei: Fix building on musl libc 2025-08-15 12:13:38 +02:00
scripts kconfig: lxdialog: fix 'space' to (de)select options 2025-08-20 18:30:48 +02:00
security apparmor: fix x_table_lookup when stacking is not the first entry 2025-08-20 18:30:47 +02:00
sound ASoC: fsl_sai: replace regmap_write with regmap_update_bits 2025-08-20 18:30:50 +02:00
tools tools/power turbostat: Handle cap_get_proc() ENOSYS 2025-08-20 18:30:49 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-07-17 18:37:08 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Linux 6.12.42 2025-08-15 12:14:14 +02:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.