[SRU][Artful][Bionic][PATCH 1/1] x86/intel_rdt/cqm: Prevent use after free

[Joseph Salisbury]

From: Thomas Gleixner <tglx at linutronix.de>

BugLink: http://bugs.launchpad.net/bugs/1733662

intel_rdt_iffline_cpu() -> domain_remove_cpu() frees memory first and then
proceeds accessing it.

 BUG: KASAN: use-after-free in find_first_bit+0x1f/0x80
 Read of size 8 at addr ffff883ff7c1e780 by task cpuhp/31/195
 find_first_bit+0x1f/0x80
 has_busy_rmid+0x47/0x70
 intel_rdt_offline_cpu+0x4b4/0x510

 Freed by task 195:
 kfree+0x94/0x1a0
 intel_rdt_offline_cpu+0x17d/0x510

Do the teardown first and then free memory.

Fixes: 24247aeeabe9 ("x86/intel_rdt/cqm: Improve limbo list processing")
Reported-by: Joseph Salisbury <joseph.salisbury at canonical.com>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: Ravi Shankar <ravi.v.shankar at intel.com>
Cc: Peter Zilstra <peterz at infradead.org>
Cc: Stephane Eranian <eranian at google.com>
Cc: Vikas Shivappa <vikas.shivappa at linux.intel.com>
Cc: Andi Kleen <ak at linux.intel.com>
Cc: "Roderick W. Smith" <rod.smith at canonical.com>
Cc: 1733662 at bugs.launchpad.net
Cc: Fenghua Yu <fenghua.yu at intel.com>
Cc: Tony Luck <tony.luck at intel.com>
Cc: stable at vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801161957510.2366@nanos

(cherry picked from commit d47924417319e3b6a728c0b690f183e75bc2a702)
Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
---
 arch/x86/kernel/cpu/intel_rdt.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index cd5fc61..c6cdc02 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -524,10 +524,6 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 		 */
 		if (static_branch_unlikely(&rdt_mon_enable_key))
 			rmdir_mondata_subdir_allrdtgrp(r, d->id);
-		kfree(d->ctrl_val);
-		kfree(d->rmid_busy_llc);
-		kfree(d->mbm_total);
-		kfree(d->mbm_local);
 		list_del(&d->list);
 		if (is_mbm_enabled())
 			cancel_delayed_work(&d->mbm_over);
@@ -544,6 +540,10 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 			cancel_delayed_work(&d->cqm_limbo);
 		}
 
+		kfree(d->ctrl_val);
+		kfree(d->rmid_busy_llc);
+		kfree(d->mbm_total);
+		kfree(d->mbm_local);
 		kfree(d);
 		return;
 	}
-- 
2.7.4