drm/vc4: kms: Clear the HVS FIFO commit pointer once done

BugLink: https://bugs.launchpad.net/bugs/1953731
commit d134c5ff71c7f2320fc7997f2fbbdedf0c76889a upstream.

Commit 9ec03d7f1ed3 ("drm/vc4: kms: Wait on previous FIFO users before a
commit") introduced a wait on the previous commit done on a given HVS
FIFO.

However, we never cleared that pointer once done. Since
drm_crtc_commit_put can free the drm_crtc_commit structure directly if
we were the last user, this means that it can lead to a use-after free
if we were to duplicate the state, and that stale pointer would even be
copied to the new state.

Set the pointer to NULL once we're done with the wait so that we don't
carry over a pointer to a free'd structure.

Fixes: 9ec03d7f1ed3 ("drm/vc4: kms: Wait on previous FIFO users before a commit")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Tested-by: Jian-Hong Pan <jhp@endlessos.org>
Link: https://lore.kernel.org/r/20211117094527.146275-5-maxime@cerno.tech
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 7c1d0c3beba2e5a3a37bb9a0488bd0a530902ad2..f80370e87e98e95e0f4fd64a7fc747df1fa907fe 100644 (file)
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -379,6 +379,7 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
                        drm_err(dev, "Timed out waiting for commit\n");
 
                drm_crtc_commit_put(commit);
+               old_hvs_state->fifo_state[channel].pending_commit = NULL;
        }
 
        if (vc4->hvs->hvs5)