[PW_SID:1095737] [v5] Bluetooth: hci_uart: fix UAF in hci_uart_tty_close()

[BluezTestBot]

From: Mingyu Wang 25181214217@stu.xidian.edu.cn

A Use-After-Free (UAF) vulnerability and a subsequent kernel panic were
observed in hci_uart_write_work() due to a race condition between the
initialization of the HCI UART line discipline and concurrent TTY hangup.

This issue was triggered by our custom device emulation and fuzzing
framework (DevGen) on the v6.18 kernel. Due to the highly timing-dependent
nature of this race condition (requiring a precise interleaving of
TIOCVHANGUP and protocol setup), Syzkaller failed to extract a reliable
standalone C reproducer (reproducer is too unreliable: 0.00).

The crash trace is as follows:
ODEBUG: free active (active state 0) object: ffff88804024e870 object type: work_struct hint: hci_uart_write_work+0x0/0x940
WARNING: CPU: 0 PID: 338273 at lib/debugobjects.c:612 debug_print_object+0x1a2/0x2b0
...
Call Trace:

debug_check_no_obj_freed+0x3ec/0x520
kfree+0x3f0/0x6c0
hci_uart_tty_close+0x127/0x2a0
k_ldisc_close+0x113/0x1a0
tty_ldisc_kill+0x8e/0x150
tty_ldisc_hangup+0x3c1/0x730
__tty_hangup.part.0+0x3fd/0x8a0
tty_ioctl+0x120f/0x1690
__x64_sys_ioctl+0x18f/0x210
do_syscall_64+0xcb/0xfa0
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The issue arises because the workqueues (init_ready and write_work) are
only flushed/cancelled if the HCI_UART_PROTO_READY flag is set. However,
during the protocol initialization phase (HCI_UART_PROTO_INIT), the
underlying protocol may schedule work. If a hangup occurs before the setup
completes and the READY flag is set, hci_uart_tty_close() skips the
teardown of these workqueues and proceeds to free the hu struct. When
the scheduled work executes later, it blindly dereferences the freed hu
struct.

Fix this by moving the workqueue teardown to the very beginning of
hci_uart_tty_close(), outside the HCI_UART_PROTO_READY check and prior to
calling hci_uart_close(). Furthermore, use disable_work_sync() instead of
cancel_work_sync() to unconditionally disable the works. This ensures that
any pending works are cancelled and no new submissions can occur before or
during the teardown of the device connection. Note that hu->init_ready and
hu->write_work are initialized in hci_uart_tty_open(), so it is always safe
to call disable_work_sync() on them in hci_uart_tty_close(), even if the
protocol was never fully attached.

Fixes: 3b79925 ("Bluetooth: hci_uart: Cancel init work before unregistering")
Cc: stable@vger.kernel.org
Signed-off-by: Mingyu Wang 25181214217@stu.xidian.edu.cn

Changes in v5:

• Moved disable_work_sync() to the very top of hci_uart_tty_close(),
  before hci_uart_close(), to prevent any concurrent re-queuing
  during device shutdown and resolve Sashiko static analysis warnings.

Changes in v4:

• Adopted Luiz's suggestion to use disable_work_sync() instead of
  cancel_work_sync() to prevent new work submissions during teardown.

Changes in v3:

• Added 'Cc: stable' tag as requested by the stable bot.

Changes in v2:

• Added KASAN/ODEBUG crash trace.

drivers/bluetooth/hci_ldisc.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

[github-actions]

CheckPatch
Desc: Run checkpatch.pl script
Duration: 1.88 seconds
Result: FAIL
Output:

[v5] Bluetooth: hci_uart: fix UAF in hci_uart_tty_close()
WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
#88: 
  ODEBUG: free active (active state 0) object: ffff88804024e870 object type: work_struct hint: hci_uart_write_work+0x0/0x940

total: 0 errors, 1 warnings, 24 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/github/workspace/src/patch/14576205.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.

[github-actions]

GitLint
Desc: Run gitlint
Duration: 0.33 seconds
Result: FAIL
Output:

[v5] Bluetooth: hci_uart: fix UAF in hci_uart_tty_close()

WARNING: I3 - ignore-body-lines: gitlint will be switching from using Python regex 'match' (match beginning) to 'search' (match anywhere) semantics. Please review your ignore-body-lines.regex option accordingly. To remove this warning, set general.regex-style-search=True. More details: https://jorisroovers.github.io/gitlint/configuration/#regex-style-search
16: B1 Line exceeds max length (124>80): "  ODEBUG: free active (active state 0) object: ffff88804024e870 object type: work_struct hint: hci_uart_write_work+0x0/0x940"
17: B1 Line exceeds max length (86>80): "  WARNING: CPU: 0 PID: 338273 at lib/debugobjects.c:612 debug_print_object+0x1a2/0x2b0"
57: B2 Line has trailing whitespace: "- Moved disable_work_sync() to the very top of hci_uart_tty_close(), "
58: B2 Line has trailing whitespace: "  before hci_uart_close(), to prevent any concurrent re-queuing "
62: B2 Line has trailing whitespace: "- Adopted Luiz's suggestion to use disable_work_sync() instead of "

[github-actions]

SubjectPrefix
Desc: Check subject contains "Bluetooth" prefix
Duration: 0.13 seconds
Result: PASS

[github-actions]

BuildKernel
Desc: Build Kernel for Bluetooth
Duration: 27.45 seconds
Result: PASS

[github-actions]

CheckAllWarning
Desc: Run linux kernel with all warning enabled
Duration: 29.64 seconds
Result: PASS

[github-actions]

CheckSparse
Desc: Run sparse tool with linux kernel
Duration: 27.83 seconds
Result: PASS

[github-actions]

BuildKernel32
Desc: Build 32bit Kernel for Bluetooth
Duration: 26.56 seconds
Result: PASS

[github-actions]

TestRunnerSetup
Desc: Setup kernel and bluez for test-runner
Duration: 586.79 seconds
Result: PASS

[github-actions]

IncrementalBuild
Desc: Incremental build with the patches in the series
Duration: 25.50 seconds
Result: PASS