My local syzbot instance hit GPF in ttm_bo_release(). Unfortunately, syzbot didn't produce a reproducer for this, but I found out possible scenario:
drm_gem_vram_create() <-- drm_gem_vram_object kzalloced (bo embedded in this object) ttm_bo_init() ttm_bo_init_reserved() ttm_resource_alloc() man->func->alloc() <-- allocation failure ttm_bo_put() ttm_bo_release() ttm_mem_io_free() <-- bo->resource == NULL passed as second argument *GPF*
Added NULL check inside ttm_mem_io_free() to prevent reported GPF and make this function NULL save in future.
Same problem was in ttm_bo_move_to_lru_tail() as Christian reported. ttm_bo_move_to_lru_tail() is called in ttm_bo_release() and mem pointer can be NULL as well as in ttm_mem_io_free().
Fail log:
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] CPU: 1 PID: 10419 Comm: syz-executor.3 Not tainted 5.13.0-rc7-next-20210625 #7 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014 RIP: 0010:ttm_mem_io_free+0x28/0x170 drivers/gpu/drm/ttm/ttm_bo_util.c:66 Code: b1 90 41 56 41 55 41 54 55 48 89 fd 53 48 89 f3 e8 cd 19 24 fd 4c 8d 6b 20 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 2a 01 00 00 4c 8b 63 20 31 ff 4c 89 e6 e8 00 1f RSP: 0018:ffffc900141df968 EFLAGS: 00010202 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc90010da0000 RDX: 0000000000000004 RSI: ffffffff84513ea3 RDI: ffff888041fbc010 RBP: ffff888041fbc010 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000020 R14: ffff88806b258800 R15: ffff88806b258a38 FS: 00007fa6e9845640(0000) GS:ffff88807ec00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fad61265e18 CR3: 000000005ad79000 CR4: 0000000000350ee0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: ttm_bo_release+0xd94/0x10a0 drivers/gpu/drm/ttm/ttm_bo.c:422 kref_put include/linux/kref.h:65 [inline] ttm_bo_put drivers/gpu/drm/ttm/ttm_bo.c:470 [inline] ttm_bo_init_reserved+0x7cb/0x960 drivers/gpu/drm/ttm/ttm_bo.c:1050 ttm_bo_init+0x105/0x270 drivers/gpu/drm/ttm/ttm_bo.c:1074 drm_gem_vram_create+0x332/0x4c0 drivers/gpu/drm/drm_gem_vram_helper.c:228
Fixes: d3116756a710 ("drm/ttm: rename bo->mem and make it a pointer") Signed-off-by: Pavel Skripkin paskripkin@gmail.com ---
Changes in v2: 1. Added NULL check in ttm_bo_move_to_lru_tail() 2. Changed subject line, since NULL check added in 2 funtions
--- drivers/gpu/drm/ttm/ttm_bo.c | 3 +++ drivers/gpu/drm/ttm/ttm_bo_util.c | 3 +++ 2 files changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c index 1b950b45cf4b..8d7fd65ccced 100644 --- a/drivers/gpu/drm/ttm/ttm_bo.c +++ b/drivers/gpu/drm/ttm/ttm_bo.c @@ -102,6 +102,9 @@ void ttm_bo_move_to_lru_tail(struct ttm_buffer_object *bo, return; }
+ if (!mem) + return; + man = ttm_manager_type(bdev, mem->mem_type); list_move_tail(&bo->lru, &man->lru[bo->priority]);
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c index 2f57f824e6db..763fa6f4e07d 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_util.c +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c @@ -63,6 +63,9 @@ int ttm_mem_io_reserve(struct ttm_device *bdev, void ttm_mem_io_free(struct ttm_device *bdev, struct ttm_resource *mem) { + if (!mem) + return; + if (!mem->bus.offset && !mem->bus.addr) return;