genirq: Validate action before dereferencing it in handle_irq_event_percpu()

debian/changelog

@@ -162,6 +162,8 @@ linux (4.4.3-1) UNRELEASED; urgency=medium
   [ Uwe Kleine-König ]
   * [armhf] enable AXP20X_POWER (Closes: #815971)
   * [rt] Update to 4.4.3-rt9
+  * genirq: Validate action before dereferencing it in
+    handle_irq_event_percpu()
 
  -- Salvatore Bonaccorso <carnil@debian.org>  Sun, 28 Feb 2016 07:02:42 +0100
 

debian/patches/bugfix/all/genirq-Validate-action-before-dereferencing-it-in-ha.patch

@@ -0,0 +1,100 @@
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Wed, 13 Jan 2016 14:07:25 +0100
+Subject: [PATCH] genirq: Validate action before dereferencing it in
+ handle_irq_event_percpu()
+Origin: v4.5-rc2, commit:570540d50710ed192e98e2f7f74578c9486b6b05
+
+commit 71f64340fc0e changed the handling of irq_desc->action from
+
+CPU 0                   CPU 1
+free_irq()              lock(desc)
+  lock(desc)            handle_edge_irq()
+                        if (desc->action) {
+                          handle_irq_event()
+                            action = desc->action
+                            unlock(desc)
+  desc->action = NULL       handle_irq_event_percpu(desc, action)
+                              action->xxx
+to
+
+CPU 0                   CPU 1
+free_irq()              lock(desc)
+  lock(desc)            handle_edge_irq()
+                        if (desc->action) {
+                          handle_irq_event()
+                            unlock(desc)
+  desc->action = NULL       handle_irq_event_percpu(desc, action)
+                              action = desc->action
+                              action->xxx
+
+So if free_irq manages to set the action to NULL between the unlock and before
+the readout, we happily dereference a null pointer.
+
+We could simply revert 71f64340fc0e, but we want to preserve the better code
+generation. A simple solution is to change the action loop from a do {} while
+to a while {} loop.
+
+This is safe because we either see a valid desc->action or NULL. If the action
+is about to be removed it is still valid as free_irq() is blocked on
+synchronize_irq().
+
+CPU 0                   CPU 1
+free_irq()              lock(desc)
+  lock(desc)            handle_edge_irq()
+                          handle_irq_event(desc)
+                            set(INPROGRESS)
+                            unlock(desc)
+                            handle_irq_event_percpu(desc)
+                            action = desc->action
+  desc->action = NULL           while (action) {
+                                  action->xxx
+                                  ...
+                                  action = action->next;
+  sychronize_irq()
+    while(INPROGRESS);      lock(desc)
+                            clr(INPROGRESS)
+free(action)
+
+That's basically the same mechanism as we have for shared
+interrupts. action->next can become NULL while handle_irq_event_percpu()
+runs. Either it sees the action or NULL. It does not matter, because action
+itself cannot go away before the interrupt in progress flag has been cleared.
+
+Fixes: commit 71f64340fc0e "genirq: Remove the second parameter from handle_irq_event_percpu()"
+Reported-by: zyjzyj2000@gmail.com
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+Cc: Huang Shijie <shijie.huang@arm.com>
+Cc: Jiang Liu <jiang.liu@linux.intel.com>
+Cc: Peter Zijlstra <peterz@infradead.org>
+Cc: stable@vger.kernel.org
+Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1601131224190.3575@nanos
+---
+ kernel/irq/handle.c | 5 +++--
+ 1 file changed, 3 insertions(+), 2 deletions(-)
+
+diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
+index a302cf9a2126..57bff7857e87 100644
+--- a/kernel/irq/handle.c
++++ b/kernel/irq/handle.c
+@@ -138,7 +138,8 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
+ 	unsigned int flags = 0, irq = desc->irq_data.irq;
+ 	struct irqaction *action = desc->action;
+ 
+-	do {
++	/* action might have become NULL since we dropped the lock */
++	while (action) {
+ 		irqreturn_t res;
+ 
+ 		trace_irq_handler_entry(irq, action);
+@@ -173,7 +174,7 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
+ 
+ 		retval |= res;
+ 		action = action->next;
+-	} while (action);
++	}
+ 
+ 	add_interrupt_randomness(irq, flags);
+ 
+-- 
+2.7.0
+

debian/patches/series

@@ -133,6 +133,7 @@ bugfix/all/af_unix-guard-against-other-sk-in-unix_dgram_sendmsg.patch
 bugfix/all/revert-workqueue-make-sure-delayed-work-run-in-local-cpu.patch
 bugfix/all/af_unix-don-t-set-err-in-unix_stream_read_generic-unless-there-was-an-error.patch
 bugfix/all/bpf-fix-branch-offset-adjustment-on-backjumps-after-.patch
+bugfix/all/genirq-Validate-action-before-dereferencing-it-in-ha.patch
 bugfix/x86/x86-mm-page-align-the-_end-symbol-to-avoid-pfn-conve.patch
 bugfix/x86/x86-mm-pat-ensure-cpa-pfn-only-contains-page-frame-n.patch
 bugfix/x86/x86-efi-map-ram-into-the-identity-page-table-for-mix.patch