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ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry

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do_mq_timedreceive calls wq_sleep with a stack local address.  The
sender (do_mq_timedsend) uses this address to later call pipelined_send.

This leads to a very hard to trigger race where a do_mq_timedreceive
call might return and leave do_mq_timedsend to rely on an invalid
address, causing the following crash:

  RIP: 0010:wake_q_add_safe+0x13/0x60
  Call Trace:
   __x64_sys_mq_timedsend+0x2a9/0x490
   do_syscall_64+0x80/0x680
   entry_SYSCALL_64_after_hwframe+0x44/0xa9
  RIP: 0033:0x7f5928e40343

The race occurs as:

1. do_mq_timedreceive calls wq_sleep with the address of `struct
   ext_wait_queue` on function stack (aliased as `ewq_addr` here) - it
   holds a valid `struct ext_wait_queue *` as long as the stack has not
   been overwritten.

2. `ewq_addr` gets added to info->e_wait_q[RECV].list in wq_add, and
   do_mq_timedsend receives it via wq_get_first_waiter(info, RECV) to call
   __pipelined_op.

3. Sender calls __pipelined_op::smp_store_release(&this->state,
   STATE_READY).  Here is where the race window begins.  (`this` is
   `ewq_addr`.)

4. If the receiver wakes up now in do_mq_timedreceive::wq_sleep, it
   will see `state == STATE_READY` and break.

5. do_mq_timedreceive returns, and `ewq_addr` is no longer guaranteed
   to be a `struct ext_wait_queue *` since it was on do_mq_timedreceive's
   stack.  (Although the address may not get overwritten until another
   function happens to touch it, which means it can persist around for an
   indefinite time.)

6. do_mq_timedsend::__pipelined_op() still believes `ewq_addr` is a
   `struct ext_wait_queue *`, and uses it to find a task_struct to pass to
   the wake_q_add_safe call.  In the lucky case where nothing has
   overwritten `ewq_addr` yet, `ewq_addr->task` is the right task_struct.
   In the unlucky case, __pipelined_op::wake_q_add_safe gets handed a
   bogus address as the receiver's task_struct causing the crash.

do_mq_timedsend::__pipelined_op() should not dereference `this` after
setting STATE_READY, as the receiver counterpart is now free to return.
Change __pipelined_op to call wake_q_add_safe on the receiver's
task_struct returned by get_task_struct, instead of dereferencing `this`
which sits on the receiver's stack.

As Manfred pointed out, the race potentially also exists in
ipc/msg.c::expunge_all and ipc/sem.c::wake_up_sem_queue_prepare.  Fix
those in the same way.

Link: https://lkml.kernel.org/r/20210510102950.12551-1-varad.gautam@suse.com
Fixes: c5b2cbdbda ("ipc/mqueue.c: update/document memory barriers")
Fixes: 8116b54e7e ("ipc/sem.c: document and update memory barriers")
Fixes: 0d97a82ba8 ("ipc/msg.c: update and document memory barriers")
Signed-off-by: Varad Gautam <varad.gautam@suse.com>
Reported-by: Matthias von Faber <matthias.vonfaber@aox-tech.de>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Varad Gautam 2021-05-22 17:41:49 -07:00 committed by Linus Torvalds
parent f10628d2f6
commit a11ddb37bf
3 changed files with 12 additions and 6 deletions
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6
ipc/mqueue.c
View File

@ -1004,12 +1004,14 @@ static inline void __pipelined_op(struct wake_q_head *wake_q,
struct mqueue_inode_info *info,
struct ext_wait_queue *this)
{
struct task_struct *task;
list_del(&this->list);
get_task_struct(this->task);
task = get_task_struct(this->task);
/* see MQ_BARRIER for purpose/pairing */
smp_store_release(&this->state, STATE_READY);
wake_q_add_safe(wake_q, this->task);
wake_q_add_safe(wake_q, task);
}
/* pipelined_send() - send a message directly to the task waiting in

6
ipc/msg.c
View File

@ -251,11 +251,13 @@ static void expunge_all(struct msg_queue *msq, int res,
struct msg_receiver *msr, *t;
list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
get_task_struct(msr->r_tsk);
struct task_struct *r_tsk;
r_tsk = get_task_struct(msr->r_tsk);
/* see MSG_BARRIER for purpose/pairing */
smp_store_release(&msr->r_msg, ERR_PTR(res));
wake_q_add_safe(wake_q, msr->r_tsk);
wake_q_add_safe(wake_q, r_tsk);
}
}

6
ipc/sem.c
View File

@ -784,12 +784,14 @@ static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
static inline void wake_up_sem_queue_prepare(struct sem_queue *q, int error,
struct wake_q_head *wake_q)
{
get_task_struct(q->sleeper);
struct task_struct *sleeper;
sleeper = get_task_struct(q->sleeper);
/* see SEM_BARRIER_2 for purpose/pairing */
smp_store_release(&q->status, error);
wake_q_add_safe(wake_q, q->sleeper);
wake_q_add_safe(wake_q, sleeper);
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)