bisecting fixing commit since 01364dad1d4577e27a57729d41053f661bb8a5b9 building syzkaller on 78267cec1aaa5e066d66e6a6c76fea1753e51b46 testing commit 01364dad1d4577e27a57729d41053f661bb8a5b9 with gcc (GCC) 8.1.0 kernel signature: 03ccfbfe3948bf8838ead8fe2a7cbafe14f0e17e30bf6691d56d0b09cd717333 all runs: crashed: KASAN: use-after-free Read in vgem_gem_dumb_create testing current HEAD a41ba30d9df20fe141c92aacbb56b6b077f19716 testing commit a41ba30d9df20fe141c92aacbb56b6b077f19716 with gcc (GCC) 8.1.0 kernel signature: 710281fc3635e0b7b55c5fc0bb89d1f27ab5751245ee5861d034c8eabc75b12a all runs: crashed: KASAN: use-after-free Read in vgem_gem_dumb_create revisions tested: 2, total time: 25m52.936314239s (build: 18m44.423001456s, test: 6m30.213909151s) the crash still happens on HEAD commit msg: Linux 4.14.181 crash: KASAN: use-after-free Read in vgem_gem_dumb_create IPv6: ADDRCONF(NETDEV_UP): batadv_slave_1: link is not ready batman_adv: batadv0: Interface activated: batadv_slave_1 IPv6: ADDRCONF(NETDEV_CHANGE): batadv_slave_1: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready ================================================================== BUG: KASAN: use-after-free in vgem_gem_dumb_create+0x1ee/0x200 drivers/gpu/drm/vgem/vgem_drv.c:215 Read of size 8 at addr ffff8880a4b506c0 by task syz-executor.0/8443 CPU: 1 PID: 8443 Comm: syz-executor.0 Not tainted 4.14.181-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0xf7/0x13b lib/dump_stack.c:58 print_address_description.cold.7+0x9/0x1c9 mm/kasan/report.c:252 kasan_report_error mm/kasan/report.c:351 [inline] kasan_report.cold.8+0x11a/0x2d3 mm/kasan/report.c:409 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430 vgem_gem_dumb_create+0x1ee/0x200 drivers/gpu/drm/vgem/vgem_drv.c:215 drm_mode_create_dumb_ioctl+0x1ea/0x2b0 drivers/gpu/drm/drm_dumb_buffers.c:92 drm_ioctl_kernel+0x133/0x1d0 drivers/gpu/drm/drm_ioctl.c:736 drm_ioctl+0x417/0x900 drivers/gpu/drm/drm_ioctl.c:836 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:500 [inline] do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x74/0x80 fs/ioctl.c:692 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb RIP: 0033:0x45c849 RSP: 002b:00007f2419821c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f24198226d4 RCX: 000000000045c849 RDX: 0000000020000000 RSI: 00000000c02064b2 RDI: 0000000000000004 RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 0000000000000289 R14: 00000000004d30a0 R15: 000000000076bf0c Allocated by task 8443: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack+0x43/0xd0 mm/kasan/kasan.c:447 set_track mm/kasan/kasan.c:459 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:551 kmem_cache_alloc_trace+0x152/0x7a0 mm/slab.c:3618 kmalloc include/linux/slab.h:488 [inline] kzalloc include/linux/slab.h:661 [inline] __vgem_gem_create+0x47/0xd0 drivers/gpu/drm/vgem/vgem_drv.c:159 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:188 [inline] vgem_gem_dumb_create+0xbf/0x200 drivers/gpu/drm/vgem/vgem_drv.c:211 drm_mode_create_dumb_ioctl+0x1ea/0x2b0 drivers/gpu/drm/drm_dumb_buffers.c:92 drm_ioctl_kernel+0x133/0x1d0 drivers/gpu/drm/drm_ioctl.c:736 drm_ioctl+0x417/0x900 drivers/gpu/drm/drm_ioctl.c:836 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:500 [inline] do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x74/0x80 fs/ioctl.c:692 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb Freed by task 8443: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack+0x43/0xd0 mm/kasan/kasan.c:447 set_track mm/kasan/kasan.c:459 [inline] kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524 __cache_free mm/slab.c:3496 [inline] kfree+0xcc/0x270 mm/slab.c:3815 vgem_gem_free_object+0xa7/0xd0 drivers/gpu/drm/vgem/vgem_drv.c:61 drm_gem_object_free+0x83/0x120 drivers/gpu/drm/drm_gem.c:838 kref_put include/linux/kref.h:70 [inline] drm_gem_object_put_unlocked+0x102/0x130 drivers/gpu/drm/drm_gem.c:867 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:193 [inline] vgem_gem_dumb_create+0xf6/0x200 drivers/gpu/drm/vgem/vgem_drv.c:211 drm_mode_create_dumb_ioctl+0x1ea/0x2b0 drivers/gpu/drm/drm_dumb_buffers.c:92 drm_ioctl_kernel+0x133/0x1d0 drivers/gpu/drm/drm_ioctl.c:736 drm_ioctl+0x417/0x900 drivers/gpu/drm/drm_ioctl.c:836 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:500 [inline] do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684 SYSC_ioctl fs/ioctl.c:701 [inline] SyS_ioctl+0x74/0x80 fs/ioctl.c:692 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb The buggy address belongs to the object at ffff8880a4b505c0 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 256 bytes inside of 512-byte region [ffff8880a4b505c0, ffff8880a4b507c0) The buggy address belongs to the page: page:ffffea000292d400 count:1 mapcount:0 mapping:ffff8880a4b500c0 index:0xffff8880a4b500c0 flags: 0xfffe0000000100(slab) raw: 00fffe0000000100 ffff8880a4b500c0 ffff8880a4b500c0 0000000100000004 raw: ffffea000257bbe0 ffffea00027e71e0 ffff8880aa800940 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880a4b50580: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb ffff8880a4b50600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff8880a4b50680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8880a4b50700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880a4b50780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ==================================================================