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

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().

Fixes: 8a6b1bc70dbb ("powerpc/eeh: EEH core to handle special event")
Cc: stable@vger.kernel.org # v3.11+
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 15 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/eeh_driver.c b/arch/powerpc/kernel/eeh_driver.c
index b94887165a10..e50d1470714f 100644
--- a/arch/powerpc/kernel/eeh_driver.c
+++ b/arch/powerpc/kernel/eeh_driver.c
@@ -724,7 +724,7 @@ static int eeh_reset_device(struct eeh_pe *pe, struct pci_bus *bus,
  */
 #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(struct eeh_pe *pe)
         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(struct eeh_pe *pe)
         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(void)
                  */
                 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();