Patch "powerpc/64s: Fix VAS mm use after free" has been added to the 5.15-stable tree

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

    powerpc/64s: Fix VAS mm use after free

to the 5.15-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-64s-fix-vas-mm-use-after-free.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f52ca4f5e116c06793936c44c6604a1facfbe464
Author: Nicholas Piggin <npiggin@xxxxxxxxx>
Date:   Wed Jun 7 20:10:24 2023 +1000

    powerpc/64s: Fix VAS mm use after free
    
    [ Upstream commit b4bda59b47879cce38a6ec5a01cd3cac702b5331 ]
    
    The refcount on mm is dropped before the coprocessor is detached.
    
    Reported-by: Sachin Sant <sachinp@xxxxxxxxxxxxx>
    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@xxxxxxxxx>
    Tested-by: Sachin Sant <sachinp@xxxxxxxxxxxxx>
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://msgid.link/20230607101024.14559-1-npiggin@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/platforms/powernv/vas-window.c b/arch/powerpc/platforms/powernv/vas-window.c
index 0072682531d80..b664838008c12 100644
--- 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 15046d80f0427..b54f6fc27896f 100644
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -441,8 +441,8 @@ static int vas_deallocate_window(struct vas_window *vwin)
 	atomic_dec(&caps->used_lpar_creds);
 	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;



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