On 2021-05-10 18:41, akpm@xxxxxxxxxxxxxxxxxxxx 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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------------------------------------------------------
From: Varad Gautam <varad.gautam@xxxxxxxx>
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@xxxxxxxx
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@xxxxxxxx>
Reported-by: Matthias von Faber <matthias.vonfaber@xxxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
