Driver code did not remove event from the list of pending events before destroy.
As a result drm core tried later 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@xxxxxxxxxxx>
---
drivers/gpu/drm/exynos/exynos_drm_crtc.c | 26 +++++++-------------------
1 file changed, 7 insertions(+), 19 deletions(-)
diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
index 50dd33d..e78c36d 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
@@ -229,24 +229,12 @@ void exynos_drm_crtc_cancel_page_flip(struct drm_crtc *crtc,
struct drm_file *file)
{
struct exynos_drm_crtc *exynos_crtc = to_exynos_crtc(crtc);
- struct drm_pending_vblank_event *e;
- unsigned long flags;
+ struct drm_pending_vblank_event *e = exynos_crtc->event;
- 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)
+ return;
+
+ exynos_crtc->event = NULL;
+ atomic_dec(&exynos_crtc->pending_update);
+ drm_event_cancel_free(crtc->dev, &e->base);
}
--
1.9.1
--
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