Commit 0c96b273 authored Jul 19, 2017 by Ethan Barnes Committed by Thomas Gleixner Jul 20, 2017

smp/hotplug: Handle removal correctly in cpuhp_store_callbacks()



If cpuhp_store_callbacks() is called for CPUHP_AP_ONLINE_DYN or
CPUHP_BP_PREPARE_DYN, which are the indicators for dynamically allocated
states, then cpuhp_store_callbacks() allocates a new dynamic state. The
first allocation in each range returns CPUHP_AP_ONLINE_DYN or
CPUHP_BP_PREPARE_DYN.

If cpuhp_remove_state() is invoked for one of these states, then there is
no protection against the allocation mechanism. So the removal, which
should clear the callbacks and the name, gets a new state assigned and
clears that one.

As a consequence the state which should be cleared stays initialized. A
consecutive CPU hotplug operation dereferences the state callbacks and
accesses either freed or reused memory, resulting in crashes.

Add a protection against this by checking the name argument for NULL. If
it's NULL it's a removal. If not, it's an allocation.

[ tglx: Added a comment and massaged changelog ]

Fixes: 5b7aa87e ("cpu/hotplug: Implement setup/removal interface")
Signed-off-by: Ethan Barnes <ethan.barnes@sandisk.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.or>
Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
Cc: Sebastian Siewior <bigeasy@linutronix.d>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/DM2PR04MB398242FC7776D603D9F99C894A60@DM2PR04MB398.namprd04.prod.outlook.com

parent 935acd3f

kernel/cpu.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -1252,7 +1252,17 @@ static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
		struct cpuhp_step *sp;
		int ret = 0;

		if (state == CPUHP_AP_ONLINE_DYN \|\| state == CPUHP_BP_PREPARE_DYN) {
		/*
		* If name is NULL, then the state gets removed.
		*
		* CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
		* the first allocation from these dynamic ranges, so the removal
		* would trigger a new allocation and clear the wrong (already
		* empty) state, leaving the callbacks of the to be cleared state
		* dangling, which causes wreckage on the next hotplug operation.
		*/
		if (name && (state == CPUHP_AP_ONLINE_DYN \|\|
		state == CPUHP_BP_PREPARE_DYN)) {
		ret = cpuhp_reserve_state(state);
		if (ret < 0)
		return ret;