From b4bda59b47879cce38a6ec5a01cd3cac702b5331 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Wed, 7 Jun 2023 20:10:24 +1000
Subject: [PATCH] powerpc/64s: Fix VAS mm use after free

References: bsc#1194869
Patch-mainline: v6.5-rc1
Git-commit: b4bda59b47879cce38a6ec5a01cd3cac702b5331

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
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/platforms/powernv/vas-window.c |    2 +-
 arch/powerpc/platforms/pseries/vas.c        |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- 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 *vwi
 	/* 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);
 	}
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -499,8 +499,8 @@ static int vas_deallocate_window(struct
 	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;