[PATCH 3.18/4.4] powerpc/eeh: Avoid use after free in eeh_handle_special_event()

[PATCH 3.18/4.4] powerpc/eeh: Avoid use after free in eeh_handle_special_event()

[Russell Currey]

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>
---
This is a backport for upstream patch daeba2956f32f91f3493788ff6ee02fb1b2f02fa
that applies to 3.18 and 4.4.
---

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

diff --git a/arch/powerpc/kernel/eeh_driver.c b/arch/powerpc/kernel/eeh_driver.c
index 247a0dc012f1..483c11aa1597 100644
--- a/arch/powerpc/kernel/eeh_driver.c
+++ b/arch/powerpc/kernel/eeh_driver.c
@@ -653,7 +653,7 @@ 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;
 	int rc = 0;
@@ -663,7 +663,7 @@ static void eeh_handle_normal_event(struct eeh_pe *pe)
 	if (!frozen_bus) {
 		pr_err("%s: Cannot find PCI bus for PHB#%d-PE#%x\n",
 			__func__, pe->phb->global_number, pe->addr);
-		return;
+		return false;
 	}
 
 	eeh_pe_update_time_stamp(pe);
@@ -788,7 +788,7 @@ 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:
 	/*
@@ -829,7 +829,11 @@ perm_error:
 		pci_lock_rescan_remove();
 		pcibios_remove_pci_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)
@@ -895,7 +899,14 @@ 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();
-- 
2.13.0

Re: [PATCH 3.18/4.4] powerpc/eeh: Avoid use after free in eeh_handle_special_event()

[Greg KH]

On Tue, Jun 06, 2017 at 05:41:55PM +1000, Russell Currey wrote:
> 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>
> ---
> This is a backport for upstream patch daeba2956f32f91f3493788ff6ee02fb1b2f02fa
> that applies to 3.18 and 4.4.

Thanks for the patch, now applied.

greg k-h