On Sat, Aug 29, 2020 at 3:24 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Aug 28, 2020 at 05:52:16AM -0700, syzbot wrote: > > syzbot has found a reproducer for the following issue on: > > > > HEAD commit: 15bc20c6 Merge tag 'tty-5.9-rc3' of git://git.kernel.org/p.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1052a669900000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=978db74cb30aa994 > > dashboard link: https://syzkaller.appspot.com/bug?extid=7a7613e5ba9ae7bd15f9 > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101c328e900000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=155eff41900000 > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+7a7613e5ba9ae7bd15f9@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > INFO: task syz-executor790:9958 blocked for more than 143 seconds. > > Not tainted 5.9.0-rc2-syzkaller #0 > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > task:syz-executor790 state:D stack:28240 pid: 9958 ppid: 6854 flags:0x00004004 > > Call Trace: > > context_switch kernel/sched/core.c:3778 [inline] > > __schedule+0x8e5/0x21e0 kernel/sched/core.c:4527 > > schedule+0xd0/0x2a0 kernel/sched/core.c:4602 > > schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1855 > > do_wait_for_common kernel/sched/completion.c:85 [inline] > > __wait_for_common kernel/sched/completion.c:106 [inline] > > wait_for_common kernel/sched/completion.c:117 [inline] > > wait_for_completion_timeout+0x15e/0x270 kernel/sched/completion.c:157 > > usb_start_wait_urb+0x144/0x2b0 drivers/usb/core/message.c:63 > > usb_bulk_msg+0x226/0x550 drivers/usb/core/message.c:254 > > do_proc_bulk+0x39b/0x710 drivers/usb/core/devio.c:1231 > > proc_bulk drivers/usb/core/devio.c:1268 [inline] > > usbdev_do_ioctl drivers/usb/core/devio.c:2542 [inline] > > usbdev_ioctl+0x586/0x3360 drivers/usb/core/devio.c:2708 > > I'm confused about this bug report. > > Here's the syz reproducer from the link listed above: > > # > https://syzkaller.appspot.com/bug?id=bf172344c5f1d3487a4feff67c3dd30e08d5b635 > # See https://goo.gl/kgGztJ for information about syzkaller reproducers. > #{"threaded":true,"repeat":true,"procs":6,"sandbox":"none","fault_call":-1,"netdev":true,"close_fds":true} > r0 = syz_open_dev$usbfs(&(0x7f0000000040)='/dev/bus/usb/00#/00#\x00', > 0x4000000000000071, 0x28081) > r1 = socket$inet6(0xa, 0x2, 0x0) > r2 = dup(r1) > ioctl$PERF_EVENT_IOC_ENABLE(r2, 0x8912, 0x400200) > socketpair$unix(0x1, 0x0, 0x0, &(0x7f0000000000)) > ioctl$USBDEVFS_CONTROL(r0, 0x8108551b, &(0x7f0000001140)={0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}) > ioctl$USBDEVFS_CLEAR_HALT(r0, 0xc0185502, &(0x7f0000000000)={0x1, 0x1}) > > As far as I can see, the only USB ioctls used in this test are > USBDEVFS_CONTROL and USBDEVFS_CLEAR_HALT. Neither of those calls > do_proc_bulk() or usb_bulk_msg(), so how did those routines end up in > the stack trace? > > In fact, do_proc_bulk() is called only for USBDEVFS_BULK. But the test > doesn't use that ioctl! > > What's going on? Am I missing part of the test? Hi Alan, Yeah, it's a bit confusing, sorry for that. Since syzkaller mutates the values that are passed into syscalls, it might mutate the cmd value of an ioctl. This results in a mismatch between the name of a syscall in syzkaller's notation, and the actual cmd value. In this case we have: ioctl$USBDEVFS_CONTROL(r0, 0x8108551b, ...) where 0x8108551b == 2164806939, which is the value for USBDEVFS_DISCONNECT_CLAIM [1], and ioctl$USBDEVFS_CLEAR_HALT(r0, 0xc0185502, ...) where 0xc0185502 == 3222820098, which is the value for USBDEVFS_BULK [2]. I remember Dmitry did some changes to this part, but I think syzkaller only avoids getting disabled ioctls during mutations. Dmitry, maybe it would make sense to avoid getting other known ioctls during mutations? Thanks! [1] https://github.com/google/syzkaller/blob/master/sys/linux/dev_bus_usb.txt.const#L13 [2] https://github.com/google/syzkaller/blob/master/sys/linux/dev_bus_usb.txt.const#L4
