In the Linux kernel, the following vulnerability has been resolved:
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:
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:
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.
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.
Sender calls __pipelined_op::smp_store_release(&this->state,
STATE_READY). Here is where the race window begins. (this is
ewq_addr.)
If the receiver wakes up now in do_mq_timedreceive::wq_sleep, it
will see state == STATE_READY and break.
do_mq_timedreceive returns, and ewq_addr is no longer guaranteed
to be a struct ext_wait_queue * since it was on do_mq_timedreceives
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.)
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 receivers 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 receivers
task_struct returned by get_task_struct, instead of dereferencing this
which sits on the receivers 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.