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>

diff --git a/arch/powerpc/kernel/eeh_driver.c b/arch/powerpc/kernel/eeh_driver.c
index b94887165a101557c97fd6a53139ae7df67dbbd9..e50d1470714fcc5a1223dc59f4be0734e4eaf611 100644 (file)
--- 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();