powerpc/64s: Fix VAS mm use after free

The refcount on mm is dropped before the coprocessor is detached.

Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Fixes: 7bc6f71bdff5f ("powerpc/vas: Define and use common vas_window struct")
Fixes: b22f2d88e435c ("powerpc/pseries/vas: Integrate API with open/close windows")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230607101024.14559-1-npiggin@gmail.com

diff --git a/arch/powerpc/platforms/powernv/vas-window.c b/arch/powerpc/platforms/powernv/vas-window.c
index 0072682..b664838 100644 (file)
--- a/arch/powerpc/platforms/powernv/vas-window.c
+++ b/arch/powerpc/platforms/powernv/vas-window.c
@@ -1310,8 +1310,8 @@ int vas_win_close(struct vas_window *vwin)
        /* if send window, drop reference to matching receive window */
        if (window->tx_win) {
                if (window->user_win) {
-                       put_vas_user_win_ref(&vwin->task_ref);
                        mm_context_remove_vas_window(vwin->task_ref.mm);
+                       put_vas_user_win_ref(&vwin->task_ref);
                }
                put_rx_win(window->rxwin);
        }

diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
index 5131804..9a44a98 100644 (file)
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -507,8 +507,8 @@ static int vas_deallocate_window(struct vas_window *vwin)
        vascaps[win->win_type].nr_open_windows--;
        mutex_unlock(&vas_pseries_mutex);
 
-       put_vas_user_win_ref(&vwin->task_ref);
        mm_context_remove_vas_window(vwin->task_ref.mm);
+       put_vas_user_win_ref(&vwin->task_ref);
 
        kfree(win);
        return 0;