bisecting fixing commit since c10b57a567e4333b9fdf60b5ec36de9859263ca2 building syzkaller on 3f3c557402456696073f79aafa65b4d7fa2b8794 testing commit c10b57a567e4333b9fdf60b5ec36de9859263ca2 with gcc (GCC) 8.1.0 kernel signature: 914d3a680c17106ccda8350c5bf30fa0cea406c764bb5b630ff12fc3484f9901 run #0: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #1: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #2: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #3: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #4: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #5: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #6: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #7: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #8: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #9: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 testing current HEAD ab9dfda232481dcfaf549ce774004d116fc80c13 testing commit ab9dfda232481dcfaf549ce774004d116fc80c13 with gcc (GCC) 8.1.0 kernel signature: 6075b4c3daffe8ef2f56bd4493bb0920a853e70f555244c6d1091d31b86cd44f run #0: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #1: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #2: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #3: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #4: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #5: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #6: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #7: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 run #8: crashed: KASAN: use-after-free Write in snd_rawmidi_kernel_write1 run #9: crashed: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 revisions tested: 2, total time: 30m3.985956036s (build: 18m44.717278549s, test: 9m33.913585397s) the crash still happens on HEAD commit msg: Linux 4.14.180 crash: KASAN: slab-out-of-bounds Write in snd_rawmidi_kernel_write1 ================================================================== BUG: KASAN: slab-out-of-bounds in _copy_from_user+0x8e/0xd0 lib/usercopy.c:12 Write of size 4096 at addr ffff8880a4efedc0 by task syz-executor.1/8583 CPU: 0 PID: 8583 Comm: syz-executor.1 Not tainted 4.14.180-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 check_memory_region_inline mm/kasan/kasan.c:260 [inline] check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278 _copy_from_user+0x8e/0xd0 lib/usercopy.c:12 copy_from_user include/linux/uaccess.h:147 [inline] snd_rawmidi_kernel_write1+0x2a0/0x5e0 sound/core/rawmidi.c:1283 snd_rawmidi_write+0x26a/0xa50 sound/core/rawmidi.c:1348 __vfs_write+0xdb/0x840 fs/read_write.c:480 vfs_write+0x150/0x4f0 fs/read_write.c:544 SYSC_write fs/read_write.c:590 [inline] SyS_write+0x100/0x250 fs/read_write.c:582 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x45c889 RSP: 002b:00007ff0c0acac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007ff0c0acb6d4 RCX: 000000000045c889 RDX: 0000000020000339 RSI: 00000000200001c0 RDI: 0000000000000003 RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 0000000000000c4e R14: 00000000004ca0d5 R15: 000000000076bf0c Allocated by task 8589: 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 __do_kmalloc mm/slab.c:3720 [inline] __kmalloc+0x15b/0x7b0 mm/slab.c:3729 kmalloc include/linux/slab.h:493 [inline] snd_rawmidi_output_params+0x156/0x3f0 sound/core/rawmidi.c:653 snd_rawmidi_ioctl+0x4b0/0x540 sound/core/rawmidi.c:764 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+0x42/0xb7 Freed by task 7752: 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 kvfree+0x2c/0x30 mm/util.c:416 seq_release fs/seq_file.c:368 [inline] single_release+0x74/0xb0 fs/seq_file.c:605 close_pdeo.part.2+0xdc/0x2b0 fs/proc/inode.c:165 close_pdeo+0xfb/0x140 include/linux/spinlock.h:317 proc_reg_release+0x10a/0x190 fs/proc/inode.c:376 __fput+0x232/0x750 fs/file_table.c:210 ____fput+0x9/0x10 fs/file_table.c:244 task_work_run+0xe5/0x170 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:191 [inline] exit_to_usermode_loop+0x16a/0x1b0 arch/x86/entry/common.c:164 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline] syscall_return_slowpath arch/x86/entry/common.c:270 [inline] do_syscall_64+0x416/0x5b0 arch/x86/entry/common.c:297 entry_SYSCALL_64_after_hwframe+0x42/0xb7 The buggy address belongs to the object at ffff8880a4efedc0 which belongs to the cache kmalloc-4096 of size 4096 The buggy address is located 0 bytes inside of 4096-byte region [ffff8880a4efedc0, ffff8880a4effdc0) The buggy address belongs to the page: page:ffffea000293bf80 count:1 mapcount:0 mapping:ffff8880a4efedc0 index:0x0 compound_mapcount: 0 flags: 0xfffe0000008100(slab|head) raw: 00fffe0000008100 ffff8880a4efedc0 0000000000000000 0000000100000001 raw: ffffea0002934120 ffffea0002939d20 ffff8880aa800dc0 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880a4eff480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff8880a4eff500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffff8880a4eff580: 00 00 00 00 00 00 00 00 00 00 00 00 02 fc fc fc ^ ffff8880a4eff600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8880a4eff680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ==================================================================