Patch "powerpc/eeh: Avoid use after free in eeh_handle_special_event()" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/eeh: Avoid use after free in eeh_handle_special_event()

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-eeh-avoid-use-after-free-in-eeh_handle_special_event.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Russell Currey <[email protected]>
Date: Wed, 19 Apr 2017 17:39:26 +1000
Subject: powerpc/eeh: Avoid use after free in eeh_handle_special_event()

From: Russell Currey <[email protected]>

commit daeba2956f32f91f3493788ff6ee02fb1b2f02fa upstream.

eeh_handle_special_event() is called when an EEH event is detected but can't be narrowed down to a specific PE. This function looks through every PE to find one in an erroneous state, then calls the regular event handler eeh_handle_normal_event() once it knows which PE has an error.

However, if eeh_handle_normal_event() found that the PE cannot possibly be recovered, it will free it, rendering the passed PE stale.
This leads to a use after free in eeh_handle_special_event() as it attempts to clear the "recovering" state on the PE after eeh_handle_normal_event() returns.

Thus, make sure the PE is valid when attempting to clear state in eeh_handle_special_event().

---
 arch/powerpc/kernel/eeh_driver.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

@@ -724,7 +724,7 @@ static int eeh_reset_device(struct eeh_p
  */
 #define MAX_WAIT_FOR_RECOVERY 300
 
-static void eeh_handle_normal_event(struct eeh_pe *pe)
+static bool eeh_handle_normal_event(struct eeh_pe *pe)
 {
 	struct pci_bus *frozen_bus;
 	struct eeh_dev *edev, *tmp;

@@ -736,7 +736,7 @@ static void eeh_handle_normal_event(stru
 	if (!frozen_bus) {
 		pr_err("%s: Cannot find PCI bus for PHB#%x-PE#%x\n",
 			__func__, pe->phb->global_number, pe->addr);
-		return;
+		return false;
 	}
 
 	eeh_pe_update_time_stamp(pe);

@@ -870,7 +870,7 @@ static void eeh_handle_normal_event(stru
 	pr_info("EEH: Notify device driver to resume\n");
 	eeh_pe_dev_traverse(pe, eeh_report_resume, NULL);
 
-	return;
+	return false;
 
 excess_failures:
 	/*

@@ -915,8 +915,12 @@ perm_error:
 			pci_lock_rescan_remove();
 			pci_hp_remove_devices(frozen_bus);
 			pci_unlock_rescan_remove();
+
+			/* The passed PE should no longer be used */
+			return true;
 		}
 	}
+	return false;
 }
 
 static void eeh_handle_special_event(void)

@@ -982,7 +986,14 @@ static void eeh_handle_special_event(voi
 		 */
 		if (rc == EEH_NEXT_ERR_FROZEN_PE ||
 		    rc == EEH_NEXT_ERR_FENCED_PHB) {
-			eeh_handle_normal_event(pe);
+			/*
+			 * eeh_handle_normal_event() can make the PE stale if it
+			 * determines that the PE cannot possibly be recovered.
+			 * Don't modify the PE state if that's the case.
+			 */
+			if (eeh_handle_normal_event(pe))
+				continue;
+
 			eeh_pe_state_clear(pe, EEH_PE_RECOVERING);
 		} else {
 			pci_lock_rescan_remove();

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/powerpc-eeh-avoid-use-after-free-in-eeh_handle_special_event.patch