We report the crash: "KASAN: use-after-free Write in vgacon_scroll"
This crash was found in v4.17-rc3. Specifically, memory access (write operation) is invalid, and it is detected by KASAN.
C repro code: https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/repro-bd11a.c kernel config: https://kiwi.cs.purdue.edu/static/alexkkid-fuzzer/kernel-config-v4.17-rc3
Crash log: ============================================================== BUG: KASAN: use-after-free in memcpy include/linux/string.h:345 [inline] BUG: KASAN: use-after-free in scr_memcpyw include/linux/vt_buffer.h:49 [inline] BUG: KASAN: use-after-free in vgacon_scrollback_update drivers/video/console/vgacon.c:249 [inline] BUG: KASAN: use-after-free in vgacon_scroll+0x684/0x890 drivers/video/console/vgacon.c:1374 Write of size 3758 at addr ffff88011a8bf98e by task syz-executor1/3226
CPU: 0 PID: 3226 Comm: syz-executor1 Not tainted 4.17.0-rc3 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xc7/0x138 lib/dump_stack.c:113 print_address_description+0x6a/0x280 mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report+0x22f/0x350 mm/kasan/report.c:412 check_memory_region_inline mm/kasan/kasan.c:260 [inline] check_memory_region+0x13b/0x1a0 mm/kasan/kasan.c:267 memcpy+0x37/0x50 mm/kasan/kasan.c:303 memcpy include/linux/string.h:345 [inline] scr_memcpyw include/linux/vt_buffer.h:49 [inline] vgacon_scrollback_update drivers/video/console/vgacon.c:249 [inline] vgacon_scroll+0x684/0x890 drivers/video/console/vgacon.c:1374 con_scroll+0x2cc/0x330 drivers/tty/vt/vt.c:329 lf+0x247/0x290 drivers/tty/vt/vt.c:1122 do_con_trol+0x14f/0x5310 drivers/tty/vt/vt.c:1785 do_con_write.part.20+0x597/0x1b70 drivers/tty/vt/vt.c:2433 do_con_write drivers/tty/vt/vt.c:2790 [inline] con_write+0xb2/0xc0 drivers/tty/vt/vt.c:2786 n_tty_write+0x763/0xea0 drivers/tty/n_tty.c:2331 do_tty_write drivers/tty/tty_io.c:958 [inline] tty_write+0x48c/0x870 drivers/tty/tty_io.c:1042 redirected_tty_write+0xaf/0xc0 drivers/tty/tty_io.c:1063 __vfs_write+0x10d/0x610 fs/read_write.c:485 vfs_write+0x187/0x500 fs/read_write.c:549 ksys_write+0xd4/0x1a0 fs/read_write.c:598 __do_sys_write fs/read_write.c:610 [inline] __se_sys_write fs/read_write.c:607 [inline] __x64_sys_write+0x73/0xb0 fs/read_write.c:607 do_syscall_64+0xa4/0x460 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x4497b9 RSP: 002b:00007fc0af9acc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007fc0af9ad6cc RCX: 00000000004497b9 RDX: 0000000000001000 RSI: 0000000020000080 RDI: 0000000000000013 RBP: 000000000071bf58 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 0000000000009ee8 R14: 00000000006f0f88 R15: 00007fc0af9ad700
The buggy address belongs to the page: page:ffffea00046a2c00 count:1 mapcount:0 mapping:0000000000000000 index:0x0 compound_mapcount: 0 flags: 0x200000000008000(head) raw: 0200000000008000 0000000000000000 0000000000000000 00000001ffffffff raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff88011a8bff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff88011a8bff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88011a8c0000: fb fb fb fc fc fb fb fb fc fc 00 00 00 fc fc fc
^ ffff88011a8c0080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88011a8c0100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ==============================================================
Thanks, Kyungtae Kim