bisecting fixing commit since 174651bdf802a2139065e8e31ce950e2f3fc4a94 building syzkaller on ab342da3f9aa45e3f2d9e872576ab5cd3e3c350b testing commit 174651bdf802a2139065e8e31ce950e2f3fc4a94 with gcc (GCC) 8.1.0 kernel signature: 051a1bef4b4fb6d0d4b2caf435ff9261f09ab8b5379e07b6adaa71ad59478fa3 run #0: crashed: KASAN: use-after-free Write in release_tty run #1: crashed: KASAN: use-after-free Write in release_tty run #2: crashed: KASAN: use-after-free Write in release_tty run #3: crashed: KASAN: use-after-free Read in tty_open run #4: crashed: KASAN: use-after-free Write in release_tty run #5: crashed: KASAN: use-after-free Read in tty_open run #6: crashed: KASAN: use-after-free Read in tty_open run #7: crashed: KASAN: use-after-free Write in release_tty run #8: crashed: KASAN: use-after-free Read in tty_open run #9: crashed: KASAN: use-after-free Read in tty_open testing current HEAD 7cdefde351b6911ec5ef39322980296c091f6c52 testing commit 7cdefde351b6911ec5ef39322980296c091f6c52 with gcc (GCC) 8.1.0 kernel signature: ff05667875405d215bb4dc033072b52710ef778c305d0cd35d48e19be63bdddc run #0: crashed: KASAN: use-after-free Write in release_tty run #1: crashed: KASAN: use-after-free Read in tty_open run #2: crashed: KASAN: use-after-free Read in tty_open run #3: crashed: KASAN: use-after-free Write in release_tty run #4: crashed: KASAN: use-after-free Write in release_tty run #5: crashed: KASAN: use-after-free Read in tty_open run #6: crashed: KASAN: use-after-free Read in tty_open run #7: crashed: KASAN: use-after-free Read in tty_open run #8: crashed: KASAN: use-after-free Read in tty_open run #9: crashed: KASAN: use-after-free Read in tty_open revisions tested: 2, total time: 29m18.329395497s (build: 18m40.861340233s, test: 9m29.252787094s) the crash still happens on HEAD commit msg: Linux 4.19.100 crash: KASAN: use-after-free Read in tty_open ================================================================== BUG: KASAN: use-after-free in constant_test_bit arch/x86/include/asm/bitops.h:317 [inline] BUG: KASAN: use-after-free in tty_port_kopened include/linux/tty.h:673 [inline] BUG: KASAN: use-after-free in tty_open_by_driver drivers/tty/tty_io.c:1960 [inline] BUG: KASAN: use-after-free in tty_open+0x940/0x990 drivers/tty/tty_io.c:2029 Read of size 8 at addr ffff888088eea680 by task syz-executor.0/26583 CPU: 1 PID: 26583 Comm: syz-executor.0 Not tainted 4.19.100-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x123/0x177 lib/dump_stack.c:118 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 constant_test_bit arch/x86/include/asm/bitops.h:317 [inline] tty_port_kopened include/linux/tty.h:673 [inline] tty_open_by_driver drivers/tty/tty_io.c:1960 [inline] tty_open+0x940/0x990 drivers/tty/tty_io.c:2029 chrdev_open+0x1ed/0x5c0 fs/char_dev.c:423 do_dentry_open+0x3f1/0x1010 fs/open.c:796 vfs_open+0x9a/0xc0 fs/open.c:905 do_last fs/namei.c:3421 [inline] path_openat+0x710/0x3e40 fs/namei.c:3537 do_filp_open+0x177/0x250 fs/namei.c:3567 do_sys_open+0x1dd/0x350 fs/open.c:1088 __do_sys_open fs/open.c:1106 [inline] __se_sys_open fs/open.c:1101 [inline] __x64_sys_open+0x79/0xb0 fs/open.c:1101 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x414411 Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01 RSP: 002b:00007ff0b79597a0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002 RAX: ffffffffffffffda RBX: 6666666666666667 RCX: 0000000000414411 RDX: 0000000000000000 RSI: 0000000000000800 RDI: 00007ff0b7959850 RBP: 000000000075bf20 R08: 000000000000000f R09: 0000000000000000 R10: 00007ff0b795a9d0 R11: 0000000000000293 R12: 00007ff0b795a6d4 R13: 00000000004cae23 R14: 00000000004e4318 R15: 00000000ffffffff Allocated by task 20985: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 kmem_cache_alloc_trace+0x152/0x740 mm/slab.c:3625 kmalloc include/linux/slab.h:515 [inline] kzalloc include/linux/slab.h:709 [inline] vc_allocate+0x1c0/0x6f0 drivers/tty/vt/vt.c:1088 con_install+0x4d/0x410 drivers/tty/vt/vt.c:3204 tty_driver_install_tty drivers/tty/tty_io.c:1226 [inline] tty_init_dev+0xdb/0x3c0 drivers/tty/tty_io.c:1339 tty_open_by_driver drivers/tty/tty_io.c:1981 [inline] tty_open+0x523/0x990 drivers/tty/tty_io.c:2029 chrdev_open+0x1ed/0x5c0 fs/char_dev.c:423 do_dentry_open+0x3f1/0x1010 fs/open.c:796 vfs_open+0x9a/0xc0 fs/open.c:905 do_last fs/namei.c:3421 [inline] path_openat+0x710/0x3e40 fs/namei.c:3537 do_filp_open+0x177/0x250 fs/namei.c:3567 do_sys_open+0x1dd/0x350 fs/open.c:1088 __do_sys_open fs/open.c:1106 [inline] __se_sys_open fs/open.c:1101 [inline] __x64_sys_open+0x79/0xb0 fs/open.c:1101 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 26581: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3503 [inline] kfree+0xcf/0x220 mm/slab.c:3822 vt_disallocate_all+0x247/0x3f0 drivers/tty/vt/vt_ioctl.c:323 vt_ioctl+0x186f/0x2130 drivers/tty/vt/vt_ioctl.c:816 tty_ioctl+0x452/0x1290 drivers/tty/tty_io.c:2669 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:501 [inline] do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688 ksys_ioctl+0x62/0x90 fs/ioctl.c:705 __do_sys_ioctl fs/ioctl.c:712 [inline] __se_sys_ioctl fs/ioctl.c:710 [inline] __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe The buggy address belongs to the object at ffff888088eea480 which belongs to the cache kmalloc-2048 of size 2048 The buggy address is located 512 bytes inside of 2048-byte region [ffff888088eea480, ffff888088eeac80) The buggy address belongs to the page: page:ffffea000223ba80 count:1 mapcount:0 mapping:ffff88812c29cc40 index:0x0 compound_mapcount: 0 flags: 0xfffe0000008100(slab|head) raw: 00fffe0000008100 ffffea0002a5e808 ffffea0001c81108 ffff88812c29cc40 raw: 0000000000000000 ffff888088eea480 0000000100000003 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888088eea580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888088eea600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888088eea680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888088eea700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888088eea780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb 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