Driver code did not remove event from the list of pending events before destroy. As a result drm core later tried to inspect invalid memory location. The patch replaces removal code with call to core helper.
The bug was detected using KASAN:
[ 10.107249] ================================================================== [ 10.107518] BUG: KASAN: use-after-free in drm_release+0xe9c/0x1000 at addr ffffffc089154a18 [ 10.107784] Read of size 8 by task modetest/103 [ 10.107931] ============================================================================= [ 10.113191] BUG kmalloc-128 (Not tainted): kasan: bad access detected [ 10.119608] ----------------------------------------------------------------------------- [ 10.119608] [ 10.129243] Disabling lock debugging due to kernel taint [ 10.134551] INFO: Allocated in drm_mode_page_flip_ioctl+0x500/0xa98 age=4 cpu=0 pid=103 [ 10.142532] alloc_debug_processing+0x18c/0x198 [ 10.147043] ___slab_alloc.constprop.28+0x360/0x380 [ 10.151906] __slab_alloc.isra.25.constprop.27+0x54/0xa0 [ 10.157197] kmem_cache_alloc_trace+0x370/0x3b0 [ 10.161709] drm_mode_page_flip_ioctl+0x500/0xa98 [ 10.166400] drm_ioctl+0x4c4/0xb68 [ 10.169787] do_vfs_ioctl+0x16c/0xeb8 [ 10.173429] SyS_ioctl+0x8c/0xa0 [ 10.176642] el0_svc_naked+0x24/0x28 [ 10.180204] INFO: Freed in exynos_drm_crtc_cancel_page_flip+0xe0/0x160 age=0 cpu=0 pid=103 [ 10.188447] free_debug_processing+0x174/0x388 [ 10.192871] __slab_free+0x2e8/0x438 [ 10.196431] kfree+0x350/0x360 [ 10.199469] exynos_drm_crtc_cancel_page_flip+0xe0/0x160 [ 10.204762] exynos_drm_preclose+0x58/0xa0 [ 10.208844] drm_release+0x1f0/0x1000 [ 10.212491] __fput+0x1c4/0x5b8 [ 10.215613] ____fput+0xc/0x18 [ 10.218654] task_work_run+0x130/0x198 [ 10.222385] do_exit+0x700/0x2278 [ 10.225681] do_group_exit+0xe4/0x2c8 [ 10.229327] SyS_exit_group+0x1c/0x20 [ 10.232973] el0_svc_naked+0x24/0x28 [ 10.236532] INFO: Slab 0xffffffbdc2a45500 objects=32 used=10 fp=0xffffffc089154a00 flags=0x4080 [ 10.245210] INFO: Object 0xffffffc089154a00 @offset=2560 fp=0xffffffc089157600 [ 10.245210] ... [ 10.384532] CPU: 0 PID: 103 Comm: modetest Tainted: G B 4.5.0-rc3-00748-gd5e2881 #271 [ 10.398325] Call trace: [ 10.400764] [<ffffffc000091428>] dump_backtrace+0x0/0x328 [ 10.406141] [<ffffffc000091764>] show_stack+0x14/0x20 [ 10.411176] [<ffffffc00089c550>] dump_stack+0xb0/0xe8 [ 10.416210] [<ffffffc000395778>] print_trailer+0xf8/0x160 [ 10.421592] [<ffffffc00039b5cc>] object_err+0x3c/0x50 [ 10.426626] [<ffffffc00039d630>] kasan_report_error+0x248/0x550 [ 10.432527] [<ffffffc00039da50>] __asan_report_load8_noabort+0x40/0x48 [ 10.439039] [<ffffffc000b5b724>] drm_release+0xe9c/0x1000 [ 10.444419] [<ffffffc0003d340c>] __fput+0x1c4/0x5b8 [ 10.449280] [<ffffffc0003d3884>] ____fput+0xc/0x18 [ 10.454055] [<ffffffc000101aa8>] task_work_run+0x130/0x198 [ 10.459522] [<ffffffc0000bc058>] do_exit+0x700/0x2278 [ 10.464557] [<ffffffc0000bdcfc>] do_group_exit+0xe4/0x2c8 [ 10.469939] [<ffffffc0000bdefc>] SyS_exit_group+0x1c/0x20 [ 10.475320] [<ffffffc000087530>] el0_svc_naked+0x24/0x28
Signed-off-by: Andrzej Hajda a.hajda@samsung.com --- v2: use exynos_crtc->event under event_lock --- drivers/gpu/drm/exynos/exynos_drm_crtc.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c index 50dd33d..785ffa6 100644 --- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c +++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c @@ -233,20 +233,15 @@ void exynos_drm_crtc_cancel_page_flip(struct drm_crtc *crtc, unsigned long flags;
spin_lock_irqsave(&crtc->dev->event_lock, flags); + e = exynos_crtc->event; if (e && e->base.file_priv == file) { exynos_crtc->event = NULL; - /* - * event will be destroyed by core part - * so below line should be removed later with core changes - */ - e->base.destroy(&e->base); - /* - * event_space will be increased by core part - * so below line should be removed later with core changes. - */ - file->event_space += sizeof(e->event); atomic_dec(&exynos_crtc->pending_update); } + spin_unlock_irqrestore(&crtc->dev->event_lock, flags); + + if (e && e->base.file_priv == file) + drm_event_cancel_free(crtc->dev, &e->base); }