linux/ipc
Jann Horn b52be557e2 ipc/sem: Fix dangling sem_array access in semtimedop race
When __do_semtimedop() goes to sleep because it has to wait for a
semaphore value becoming zero or becoming bigger than some threshold, it
links the on-stack sem_queue to the sem_array, then goes to sleep
without holding a reference on the sem_array.

When __do_semtimedop() comes back out of sleep, one of two things must
happen:

 a) We prove that the on-stack sem_queue has been disconnected from the
    (possibly freed) sem_array, making it safe to return from the stack
    frame that the sem_queue exists in.

 b) We stabilize our reference to the sem_array, lock the sem_array, and
    detach the sem_queue from the sem_array ourselves.

sem_array has RCU lifetime, so for case (b), the reference can be
stabilized inside an RCU read-side critical section by locklessly
checking whether the sem_queue is still connected to the sem_array.

However, the current code does the lockless check on sem_queue before
starting an RCU read-side critical section, so the result of the
lockless check immediately becomes useless.

Fix it by doing rcu_read_lock() before the lockless check.  Now RCU
ensures that if we observe the object being on our queue, the object
can't be freed until rcu_read_unlock().

This bug is only hittable on kernel builds with full preemption support
(either CONFIG_PREEMPT or PREEMPT_DYNAMIC with preempt=full).

Fixes: 370b262c89 ("ipc/sem: avoid idr tree lookup for interrupted semop")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-12-05 10:54:44 -08:00
..
compat.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ipc_sysctl.c ipc: Remove extra braces 2022-05-03 17:25:58 -05:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mq_sysctl.c ipc: Store mqueue sysctls in the ipc namespace 2022-03-08 13:39:40 -06:00
mqueue.c - hfs and hfsplus kmap API modernization from Fabio Francesco 2022-10-12 11:00:22 -07:00
msg.c ipc/msg.c: fix percpu_counter use after free 2022-10-28 13:37:22 -07:00
msgutil.c ipc: Use generic ns_common::count 2020-08-19 14:13:52 +02:00
namespace.c ipc/msg: mitigate the lock contention with percpu counter 2022-10-03 14:21:44 -07:00
sem.c ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-05 10:54:44 -08:00
shm.c ipc/shm: call underlying open/close vm_ops 2022-11-22 18:50:42 -08:00
syscall.c y2038: remove CONFIG_64BIT_TIME 2019-11-15 14:38:27 +01:00
util.c ipc/util.c: cleanup and improve sysvipc_find_ipc() 2022-09-11 21:55:05 -07:00
util.h ipc/msg: mitigate the lock contention with percpu counter 2022-10-03 14:21:44 -07:00