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. 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
