Hi Weiteng Chen, Yu Hao, On Mon, Jul 03, 2023 at 09:07:38PM -0700, Weiteng Chen wrote: > Hi Joey, > > Sorry for my late response. > > https://elixir.bootlin.com/linux/v6.3-rc7/source/drivers/bluetooth/hci_ldisc.c#L764 > > switch (cmd) { > case HCIUARTSETPROTO: > if (!test_and_set_bit(HCI_UART_PROTO_SET, &hu->flags)) { > printk(“test_and_set_bit…”) // insert a prink to make the race easy to trigger > err = hci_uart_set_proto(hu, arg); > if (err) > clear_bit(HCI_UART_PROTO_SET, &hu->flags); > } else > err = -EBUSY; > break; > > case HCIUARTGETPROTO: > if (test_bit(HCI_UART_PROTO_SET, &hu->flags)) > err = hu->proto->id; ←- null pointer deference > else > err = -EUNATCH; > break; > > This is a race condition between HCIUARTSETPROTO and HCIUARTGETPROTO. HCI_UART_PROTO_SET is set before hu->proto is set and thus it may dereference a null pointer. > > To easily trigger this bug, I inserted a prink in the source code so that the C producer can easily trigger the bug. Please let me know if you have any questions. > Thanks! I can reproduce the issue now. Weiteng, Yu Hao, do you have plan for sending patch to fix this problem? Joey Lee > Best, > Weiteng Chen > > > On Jul 3, 2023, at 8:01 PM, joeyli <jlee@xxxxxxxx> wrote: > > > > Hi, > > > > On Wed, Jun 28, 2023 at 06:57:47PM -0700, Yu Hao wrote: > >> Hi Weiteng, > >> > >> Could you give more info about the bug, e.g., kernel configuration, > >> qemu arguments. > >> > > > > Base on kernel code, looks that the HCIUARTSETPROTO and HCIUARTGETPROTO > > blocks in hci_uart_tty_ioctl() should use hci_uart->proto_lock. > > > > I have run the C reproducer a couple of days in qemu, but it did not > > reproduce issue until now. > > > > Does anyone know how to reproduce this issue easily? > > > > Thanks > > Joey Lee > >> > >> On Wed, Jun 28, 2023 at 8:02 AM joeyli <jlee@xxxxxxxx> wrote: > >>> > >>> Hi Yu Hao, > >>> > >>> I am looking at your "BUG: general protection fault in hci_uart_tty_ioctl": > >>> > >>> https://lore.kernel.org/all/CA+UBctC3p49aTgzbVgkSZ2+TQcqq4fPDO7yZitFT5uBPDeCO2g@xxxxxxxxxxxxxx/ > >>> > >>> I am trying the C reproducer in your URL, but it is not success yet: > >>> https://gist.github.com/ZHYfeng/a3e3ff2bdfea5ed5de5475f0b54d55cb > >>> > >>> I am using v6.2 mainline kernel to run the C reproducer. > >>> > >>> Could you please provide suggestions for how to reproduce this issue? > >>> And what is your qemu environment for reproducing issue? > >>> > >>> Thanks a lot! > >>> Joey Lee
