From mboxrd@z Thu Jan 1 00:00:00 1970 From: gregkh at linuxfoundation.org (Greg KH) Date: Thu, 3 Oct 2019 21:56:27 +0200 Subject: [Linux-kernel-mentees] [SYZBOT REPORT] divide error in usbtmc_generic_read In-Reply-To: <20191003193016.GA21429@localhost.localdomain> References: <20191003193016.GA21429@localhost.localdomain> Message-ID: <20191003195627.GA3590105@kroah.com> List-Id: On Fri, Oct 04, 2019 at 01:00:16AM +0530, Jaskaran Singh wrote: > Hi, > > Following is my analysis of syzbot report: > https://syzkaller.appspot.com/bug?id=688d05e810900459b03c82fb48dc609edbbf7df9 > > The bug pertains to a divide error. The report's call trace is as follows: > > usbtmc_ioctl_generic_read drivers/usb/class/usbtmc.c:1029 [inline] > usbtmc_ioctl+0x27d/0x2ab0 drivers/usb/class/usbtmc.c:2089 > vfs_ioctl fs/ioctl.c:46 [inline] > file_ioctl fs/ioctl.c:509 [inline] > do_vfs_ioctl+0xd2d/0x1330 fs/ioctl.c:696 > ksys_ioctl+0x9b/0xc0 fs/ioctl.c:713 > __do_sys_ioctl fs/ioctl.c:720 [inline] > __se_sys_ioctl fs/ioctl.c:718 [inline] > __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:718 > do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > The file:line where the error occurs is this: > drivers/usb/class/usbtmc.c:816 > > Line 816 of that file is as follows: > if ((max_transfer_size % data->wMaxPacketSize) == 0) > > Running a 'git blame' on the file in question reveals that the last > modification to line 816 was commit bb99794a4792068cb4bfd40e99e0f9d8fe7872fa. > The commit adds the USBTMC_IOCTL_READ call for the driver, and thus the > usbtmc_generic_read function. > > I was not able to reproduce the error using my native machine and the > same gcc version used by syzkaller (gcc 9.0.0 20181231). However, the > error probably occurs because data->wMaxPacketSize is zero. > > An intuitive fix for this seems to be: > > - if ((max_transfer_size % data->wMaxPacketSize) == 0) > + if (data->wMaxPacketSize && > + (max_transfer_size % data->wMaxPacketSize) == 0) > > Or perhaps introduce a guard condition above line 816 to raise an error. Yes, if wMaxPacketSize is 0, then the code should just return an error. Care to make up a patch for this and submit it to syzbot to see if it solves the problem or not? thanks, greg k-h From mboxrd@z Thu Jan 1 00:00:00 1970 From: gregkh@linuxfoundation.org (Greg KH) Date: Thu, 3 Oct 2019 21:56:27 +0200 Subject: [Linux-kernel-mentees] [SYZBOT REPORT] divide error in usbtmc_generic_read In-Reply-To: <20191003193016.GA21429@localhost.localdomain> References: <20191003193016.GA21429@localhost.localdomain> Message-ID: <20191003195627.GA3590105@kroah.com> List-Id: Content-Type: text/plain; charset="UTF-8" Message-ID: <20191003195627.pDMKINeU6PagQVAPW86k5ZTt5glsS7SP3nEJI7YxAXE@z> On Fri, Oct 04, 2019 at 01:00:16AM +0530, Jaskaran Singh wrote: > Hi, > > Following is my analysis of syzbot report: > https://syzkaller.appspot.com/bug?id=688d05e810900459b03c82fb48dc609edbbf7df9 > > The bug pertains to a divide error. The report's call trace is as follows: > > usbtmc_ioctl_generic_read drivers/usb/class/usbtmc.c:1029 [inline] > usbtmc_ioctl+0x27d/0x2ab0 drivers/usb/class/usbtmc.c:2089 > vfs_ioctl fs/ioctl.c:46 [inline] > file_ioctl fs/ioctl.c:509 [inline] > do_vfs_ioctl+0xd2d/0x1330 fs/ioctl.c:696 > ksys_ioctl+0x9b/0xc0 fs/ioctl.c:713 > __do_sys_ioctl fs/ioctl.c:720 [inline] > __se_sys_ioctl fs/ioctl.c:718 [inline] > __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:718 > do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > The file:line where the error occurs is this: > drivers/usb/class/usbtmc.c:816 > > Line 816 of that file is as follows: > if ((max_transfer_size % data->wMaxPacketSize) == 0) > > Running a 'git blame' on the file in question reveals that the last > modification to line 816 was commit bb99794a4792068cb4bfd40e99e0f9d8fe7872fa. > The commit adds the USBTMC_IOCTL_READ call for the driver, and thus the > usbtmc_generic_read function. > > I was not able to reproduce the error using my native machine and the > same gcc version used by syzkaller (gcc 9.0.0 20181231). However, the > error probably occurs because data->wMaxPacketSize is zero. > > An intuitive fix for this seems to be: > > - if ((max_transfer_size % data->wMaxPacketSize) == 0) > + if (data->wMaxPacketSize && > + (max_transfer_size % data->wMaxPacketSize) == 0) > > Or perhaps introduce a guard condition above line 816 to raise an error. Yes, if wMaxPacketSize is 0, then the code should just return an error. Care to make up a patch for this and submit it to syzbot to see if it solves the problem or not? thanks, greg k-h