Re: + ipc-mqueue-msg-sem-avoid-relying-on-a-stack-reference-past-its-expiry.patch added to -mm tree

[Davidlohr Bueso <dbueso@suse.de>]

On 2021-05-10 18:41, akpm@linux-foundation.org wrote:
> The patch titled
>      Subject: ipc/mqueue, msg, sem: Avoid relying on a stack reference
> past its expiry
> has been added to the -mm tree.  Its filename is
>      
> ipc-mqueue-msg-sem-avoid-relying-on-a-stack-reference-past-its-expiry.patch
> 
> This patch should soon appear at
> 
> https://ozlabs.org/~akpm/mmots/broken-out/ipc-mqueue-msg-sem-avoid-relying-on-a-stack-reference-past-its-expiry.patch
> and later at
> 
> https://ozlabs.org/~akpm/mmotm/broken-out/ipc-mqueue-msg-sem-avoid-relying-on-a-stack-reference-past-its-expiry.patch
> 
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> 
> *** Remember to use Documentation/process/submit-checklist.rst when
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> 
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> 
> ------------------------------------------------------
> From: Varad Gautam <varad.gautam@suse.com>
> Subject: ipc/mqueue, msg, sem: Avoid relying on a stack reference past
> its expiry
> 
> 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:
> 
> [  240.739977] RIP: 0010:wake_q_add_safe+0x13/0x60
> [  240.739991] Call Trace:
> [  240.739999]  __x64_sys_mq_timedsend+0x2a9/0x490
> [  240.740003]  ? auditd_test_task+0x38/0x40
> [  240.740007]  ? auditd_test_task+0x38/0x40
> [  240.740011]  do_syscall_64+0x80/0x680
> [  240.740017]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [  240.740019] 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: c5b2cbdbdac563 ("ipc/mqueue.c: update/document memory barriers")
> Fixes: 8116b54e7e23ef ("ipc/sem.c: document and update memory 
> barriers")
> Fixes: 0d97a82ba830d8 ("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>
> Cc: Christian Brauner <christian.brauner@ubuntu.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Manfred Spraul <manfred@colorfullife.com>
> Cc: Davidlohr Bueso <dbueso@suse.de>
> Cc: Manfred Spraul <manfred@colorfullife.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Acked-by: Davidlohr Bueso <dbueso@suse.de>