[PATCH v5 0/6] Bluetooth: fix locking and socket killing in SCO and RFCOMM

Desmond Cheong Zhi Xi desmondcheongzx at gmail.com
Wed Aug 4 11:03:02 UTC 2021


This patch series started out as a fix for "inconsistent lock state in
sco_sock_timeout" reported by Syzbot [1].

Patch 1 is sufficient to fix this error. This was also confirmed by the
reproducer for "BUG: corrupted list in kobject_add_internal (3)" [2]
which consistently hits the inconsistent lock state error.

However, while testing the proposed fix, the reproducer for [1] would
randomly return a human-unreadable error [3]. After further
investigation, this bug seems to be caused by an unrelated error with
forking [4].

While trying to fix the mysterious error, additional fixes were added,
such as switching to lock_sock and serializing _{set,clear}_timer.

Additionally, as the reproducer kept hitting the oom-killer, a fix for
SCO socket killing was also added.

The reproducer for [1] was robust enough to catch errors with these
additional fixes, hence all the patches in this series were squashed then
tested with the reproducer for [1].

Overall, this series makes the following changes:

- Patch 1: Schedule SCO sock timeouts with delayed_work to avoid
inconsistent lock usage (removes SOFTIRQs from SCO)

- Patch 2: Avoid a circular dependency between hci_dev_lock and
lock_sock (enables the switch to lock_sock)

- Patch 3: Switch to lock_sock in SCO now that SOFTIRQs and potential
deadlocks are removed

- Patch 4: Serialize calls to sco_sock_{set,clear}_timer

- Patch 5: Switch to lock_sock in RFCOMM

- Patch 6: fix SCO socket killing

v4 -> v5:
- Renamed the delayed_work variable, moved checks for sco_pi(sk)->conn
into sco_sock_{clear,set}_timer, as suggested by Luiz Augusto von Dentz
and Marcel Holtmann.
- Added check for conn->sk in sco_sock_timeout, accompanied by a
sock_hold to avoid UAF errors.
- Added check to flush work items before freeing conn.
- Avoid a circular dependency between hci_dev_lock and lock_sock.
- Switch to lock_sock in SCO, as suggested by Marcel Holtmann.
- Serial calls to sco_sock_{set,clear}_timer.
- Switch to lock_sock in RFCOMM, as suggested by Marcel Holtmann.
- Add a fix for SCO socket killing.

v3 -> v4:
- Switch to using delayed_work to schedule SCO sock timeouts instead
of using local_bh_disable. As suggested by Luiz Augusto von Dentz.

v2 -> v3:
- Split SCO and RFCOMM code changes, as suggested by Luiz Augusto von
- Simplify local bh disabling in SCO by using local_bh_disable/enable
inside sco_chan_del since local_bh_disable/enable pairs are reentrant.

v1 -> v2:
- Instead of pulling out the clean-up code out from sco_chan_del and
using it directly in sco_conn_del, disable local softirqs for relevant
- Disable local softirqs more thoroughly for instances of
bh_lock_sock/bh_lock_sock_nested in the bluetooth subsystem.
Specifically, the calls in af_bluetooth.c and rfcomm/sock.c are now made
with local softirqs disabled as well.

Link: https://syzkaller.appspot.com/bug?id=9089d89de0502e120f234ca0fc8a703f7368b31e [1]

Link: https://syzkaller.appspot.com/bug?extid=66264bf2fd0476be7e6c [2]

Link: https://syzkaller.appspot.com/text?tag=CrashReport&x=172d819a300000 [3]

Link: https://syzkaller.appspot.com/bug?id=e1bf7ba90d8dafcf318666192aba1cfd65507377 [4]

Best wishes,

Desmond Cheong Zhi Xi (6):
  Bluetooth: schedule SCO timeouts with delayed_work
  Bluetooth: avoid circular locks in sco_sock_connect
  Bluetooth: switch to lock_sock in SCO
  Bluetooth: serialize calls to sco_sock_{set,clear}_timer
  Bluetooth: switch to lock_sock in RFCOMM
  Bluetooth: fix repeated calls to sco_sock_kill

 net/bluetooth/rfcomm/sock.c |   8 +--
 net/bluetooth/sco.c         | 107 +++++++++++++++++++++---------------
 2 files changed, 66 insertions(+), 49 deletions(-)


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