On Thu, Dec 12, 2019 at 11:57 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Dec 06, 2019 at 10:25:08PM -0800, syzbot wrote: > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 7ada90eb Merge tag 'drm-next-2019-12-06' of git://anongit... > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=123ec282e00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=f07a23020fd7d21a > > dashboard link: https://syzkaller.appspot.com/bug?extid=f4f1e871965064ae689e > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17ab090ee00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f127f2e00000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+f4f1e871965064ae689e@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > BUG: kernel NULL pointer dereference, address: 0000000000000002 > > #PF: supervisor write access in kernel mode > > #PF: error_code(0x0002) - not-present page > > PGD 9764a067 P4D 9764a067 PUD 9f995067 PMD 0 > > Oops: 0002 [#1] PREEMPT SMP KASAN > > CPU: 0 PID: 9687 Comm: syz-executor433 Not tainted 5.4.0-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > Google 01/01/2011 > > RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline] > > RIP: 0010:mem_serial_out+0x70/0x90 drivers/tty/serial/8250/8250_port.c:408 > > Code: e9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 > > c1 ea 03 d3 e3 80 3c 02 00 75 19 48 63 db 49 03 5c 24 40 <44> 88 2b 5b 41 5c > > 41 5d 5d c3 e8 81 ed cf fd eb c0 e8 da ed cf fd > > RSP: 0018:ffffc90001de78e8 EFLAGS: 00010202 > > RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000 > > RDX: 1ffffffff181f40e RSI: ffffffff83e28776 RDI: ffffffff8c0fa070 > > RBP: ffffc90001de7900 R08: ffff8880919dc340 R09: ffffed10431ee1c6 > > R10: ffffed10431ee1c5 R11: ffff888218f70e2b R12: ffffffff8c0fa030 > > R13: 0000000000000001 R14: ffffc90001de7a40 R15: ffffffff8c0fa188 > > FS: 0000000001060880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000000000002 CR3: 000000009e6b8000 CR4: 00000000001406f0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > serial_out drivers/tty/serial/8250/8250.h:118 [inline] > > serial8250_clear_fifos.part.0+0x3a/0xb0 > > drivers/tty/serial/8250/8250_port.c:557 > > serial8250_clear_fifos drivers/tty/serial/8250/8250_port.c:556 [inline] > > serial8250_do_startup+0x426/0x1cf0 drivers/tty/serial/8250/8250_port.c:2121 > > serial8250_startup+0x62/0x80 drivers/tty/serial/8250/8250_port.c:2329 > > uart_port_startup drivers/tty/serial/serial_core.c:219 [inline] > > uart_startup drivers/tty/serial/serial_core.c:258 [inline] > > uart_startup+0x452/0x980 drivers/tty/serial/serial_core.c:249 > > uart_set_info drivers/tty/serial/serial_core.c:998 [inline] > > uart_set_info_user+0x13b4/0x1cf0 drivers/tty/serial/serial_core.c:1023 > > tty_tiocsserial drivers/tty/tty_io.c:2506 [inline] > > tty_ioctl+0xf60/0x14f0 drivers/tty/tty_io.c:2648 > > vfs_ioctl fs/ioctl.c:47 [inline] > > file_ioctl fs/ioctl.c:545 [inline] > > do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732 > > ksys_ioctl+0xab/0xd0 fs/ioctl.c:749 > > __do_sys_ioctl fs/ioctl.c:756 [inline] > > __se_sys_ioctl fs/ioctl.c:754 [inline] > > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754 > > do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > RIP: 0033:0x440219 > > Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 > > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff > > 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00 > > RSP: 002b:00007ffced648c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > > RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440219 > > RDX: 0000000020000240 RSI: 000000000000541f RDI: 0000000000000003 > > RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8 > > R10: 0000000000401b30 R11: 0000000000000246 R12: 0000000000401aa0 > > R13: 0000000000401b30 R14: 0000000000000000 R15: 0000000000000000 > > Modules linked in: > > CR2: 0000000000000002 > > ---[ end trace eaa11ffe82f3a763 ]--- > > RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline] > > RIP: 0010:mem_serial_out+0x70/0x90 drivers/tty/serial/8250/8250_port.c:408 > > Code: e9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 > > c1 ea 03 d3 e3 80 3c 02 00 75 19 48 63 db 49 03 5c 24 40 <44> 88 2b 5b 41 5c > > 41 5d 5d c3 e8 81 ed cf fd eb c0 e8 da ed cf fd > > RSP: 0018:ffffc90001de78e8 EFLAGS: 00010202 > > RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000 > > RDX: 1ffffffff181f40e RSI: ffffffff83e28776 RDI: ffffffff8c0fa070 > > RBP: ffffc90001de7900 R08: ffff8880919dc340 R09: ffffed10431ee1c6 > > R10: ffffed10431ee1c5 R11: ffff888218f70e2b R12: ffffffff8c0fa030 > > R13: 0000000000000001 R14: ffffc90001de7a40 R15: ffffffff8c0fa188 > > FS: 0000000001060880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000000000002 CR3: 000000009e6b8000 CR4: 00000000001406f0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > > You set up a dubious memory base for your uart and then get upset when > you write to that location. > > I don't know what to really do about this, this is a root-only operation > and you are expected to know what you are doing when you attempt this. Hi Greg, Thanks for looking into this! Should we restrict the fuzzer from accessing /dev/ttyS* entirely? Or only restrict TIOCSSERIAL on them? Something else?
