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authorEthan Barnes <Ethan.Barnes@wdc.com>2017-07-19 22:36:00 +0000
committerThomas Gleixner <tglx@linutronix.de>2017-07-20 16:40:24 +0200
commit0c96b27305faf06c068b45e07d28336c80dac286 (patch)
tree742cdb7ed22ee723b052459da704c810b27fc8d2 /kernel/cpu.c
parent935acd3f5ebc34984bd4de075e0f83e6ea10c28d (diff)
downloadlinux-0c96b27305faf06c068b45e07d28336c80dac286.tar.bz2
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: 5b7aa87e0482 ("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
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index eee033134262..a88c29ab09be 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -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;