The ast driver inherits from DRM's CRTC state, but still uses the atomic helper for struct drm_crtc_funcs.reset, drm_atomic_helper_crtc_reset().

The helper only allocates enough memory for the core CRTC state. That results in an out-ouf-bounds access when duplicating the initial CRTC state. Simplified backtrace shown below:

[ 21.469321] ================================================================== [ 21.469434] BUG: KASAN: slab-out-of-bounds in ast_crtc_atomic_duplicate_state+0x84/0x100 [ast] [ 21.469445] Read of size 8 at addr ffff888036c1c5f8 by task systemd-udevd/382 [ 21.469451] [ 21.469464] CPU: 2 PID: 382 Comm: systemd-udevd Tainted: G E 5.5.0-rc6-1-default+ #214 [ 21.469473] Hardware name: Sun Microsystems SUN FIRE X2270 M2/SUN FIRE X2270 M2, BIOS 2.05 07/01/2010 [ 21.469480] Call Trace: [ 21.469501] dump_stack+0xb8/0x110 [ 21.469528] print_address_description.constprop.0+0x1b/0x1e0 [ 21.469557] ? ast_crtc_atomic_duplicate_state+0x84/0x100 [ast] [ 21.469581] ? ast_crtc_atomic_duplicate_state+0x84/0x100 [ast] [ 21.469597] __kasan_report.cold+0x1a/0x35 [ 21.469640] ? ast_crtc_atomic_duplicate_state+0x84/0x100 [ast] [ 21.469665] kasan_report+0xe/0x20 [ 21.469693] ast_crtc_atomic_duplicate_state+0x84/0x100 [ast] [ 21.469733] drm_atomic_get_crtc_state+0xbf/0x1c0 [ 21.469768] __drm_atomic_helper_set_config+0x81/0x5a0 [ 21.469803] ? drm_atomic_plane_check+0x690/0x690 [ 21.469843] ? drm_client_rotation+0xae/0x240 [ 21.469876] drm_client_modeset_commit_atomic+0x230/0x390 [ 21.469888] ? __mutex_lock+0x8f0/0xbe0 [ 21.469929] ? drm_client_firmware_config.isra.0+0xa60/0xa60 [ 21.469948] ? drm_client_modeset_commit_force+0x28/0x230 [ 21.470031] ? memset+0x20/0x40 [ 21.470078] drm_client_modeset_commit_force+0x90/0x230 [ 21.470110] drm_fb_helper_restore_fbdev_mode_unlocked+0x5f/0xc0 [ 21.470132] drm_fb_helper_set_par+0x59/0x70 [ 21.470155] fbcon_init+0x61d/0xad0 [ 21.470185] ? drm_fb_helper_restore_fbdev_mode_unlocked+0xc0/0xc0 [ 21.470232] visual_init+0x187/0x240 [ 21.470266] do_bind_con_driver+0x2e3/0x460 [ 21.470321] do_take_over_console+0x20a/0x290 [ 21.470371] do_fbcon_takeover+0x85/0x100 [ 21.470402] register_framebuffer+0x2fd/0x490 [ 21.470425] ? kzalloc.constprop.0+0x10/0x10 [ 21.470503] __drm_fb_helper_initial_config_and_unlock+0xf2/0x140 [ 21.470533] drm_fbdev_client_hotplug+0x162/0x250 [ 21.470563] drm_fbdev_generic_setup+0xd2/0x155 [ 21.470602] ast_driver_load+0x688/0x850 [ast] <...> [ 21.472625] ==================================================================

Allocating enough memory for struct ast_crtc_state in a custom ast CRTC reset handler fixes the problem.

v2: * implement according to drm_atomic_helper_crtc_reset() * update state with __drm_atomic_helper_crtc_reset()

Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 83be6a3ceb11 ("drm/ast: Introduce struct ast_crtc_state") Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Cc: Gerd Hoffmann kraxel@redhat.com Cc: Dave Airlie airlied@redhat.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Alex Deucher alexander.deucher@amd.com Cc: "Noralf Trønnes" noralf@tronnes.org Cc: Sam Ravnborg sam@ravnborg.org Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com --- drivers/gpu/drm/ast/ast_mode.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c index 34608f0499eb..6e71cc797109 100644 --- a/drivers/gpu/drm/ast/ast_mode.c +++ b/drivers/gpu/drm/ast/ast_mode.c @@ -882,6 +882,17 @@ static const struct drm_crtc_helper_funcs ast_crtc_helper_funcs = { .atomic_disable = ast_crtc_helper_atomic_disable, };

+static void ast_crtc_reset(struct drm_crtc *crtc) +{ + struct ast_crtc_state *ast_state = + kzalloc(sizeof(*ast_state), GFP_KERNEL); + + if (crtc->state) + crtc->funcs->atomic_destroy_state(crtc, crtc->state); + + __drm_atomic_helper_crtc_reset(crtc, &ast_state->base); +} + static void ast_crtc_destroy(struct drm_crtc *crtc) { drm_crtc_cleanup(crtc); @@ -920,7 +931,7 @@ static void ast_crtc_atomic_destroy_state(struct drm_crtc *crtc, }

static const struct drm_crtc_funcs ast_crtc_funcs = { - .reset = drm_atomic_helper_crtc_reset, + .reset = ast_crtc_reset, .set_config = drm_crtc_helper_set_config, .gamma_set = drm_atomic_helper_legacy_gamma_set, .destroy = ast_crtc_destroy,