[PATCH 6.4 477/800] powerpc/64s: Fix VAS mm use after free

Greg Kroah-Hartman
2023-07-16T20:15:12Z

From: Nicholas Piggin <npiggin@gmail.com>

[ Upstream 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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/platforms/powernv/vas-window.c | 2 +-
arch/powerpc/platforms/pseries/vas.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

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 513180467562b..9a44a98ba3420 100644
--- 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;
--
2.39.2