On 21-11-24 06:11 pm, 胡连勤 wrote: > From: Lianqin Hu <hulianqin@xxxxxxxx> > > Considering that in some extreme cases, > when u_serial driver is accessed by multiple threads, > Thread A is executing the open operation and calling the gs_open, > Thread B is executing the disconnect operation and calling the > gserial_disconnect function,The port->port_usb pointer will be set to NULL. > > E.g. > Thread A Thread B > > gs_open() gadget_unbind_driver() > You can remove these extra lines. > gs_start_io() composite_disconnect() > > gs_start_rx() gserial_disconnect() > ... ... > spin_unlock(&port->port_lock) > status = usb_ep_queue() spin_lock(&port->port_lock) > spin_lock(&port->port_lock) port->port_usb = NULL > gs_free_requests(port->port_usb->in) spin_unlock(&port->port_lock) > Crash > > This causes thread A to access a null pointer (port->port_usb is null) > when calling the gs_free_requests function, causing a crash. > > To avoid this, add a null pointer check to gs_start_io before attempting > to access the value of the pointer port->port_usb. > > Unable to handle kernel NULL pointer dereference at > virtual address 00000000000000e8 > pc : gs_start_io+0x164/0x25c > lr : gs_start_io+0x238/0x25c > sp : ffffffc08b75ba00 > x29: ffffffc08b75ba00 x28: ffffffed8ba01000 x27: 0000000000020902 > x26: dead000000000100 x25: ffffff899f43a400 x24: ffffff8862325400 > x23: ffffff88623256a4 x22: ffffff8862325690 x21: ffffff88623255ec > x20: ffffff88623255d8 x19: ffffff885e19d700 x18: ffffffed8c45ae40 > x17: 00000000d48d30ad x16: 00000000d48d30ad x15: 0010000000000001 > x14: ffffffed8c50fcc0 x13: 0000000040000000 x12: 0000000000000001 > x11: 0000000080200012 x10: 0000000080200012 x9 : ffffff88623255d8 > x8 : 0000000000000000 x7 : 0000000000000000 x6 : 000000000000003f > x5 : ffffffed8ae0b9a4 x4 : fffffffe267d0ea0 x3 : 0000000080200012 > x2 : ffffff899f43a400 x1 : 0000000080200013 x0 : ffffff899f43b100 These address lists can also omitted. And the below stack can be shortened. > Call trace: > gs_start_io+0x164/0x25c > gs_open+0x108/0x13c > tty_open+0x314/0x638 > chrdev_open+0x1b8/0x258 > do_dentry_open+0x2c4/0x700 > vfs_open+0x2c/0x3c > path_openat+0xa64/0xc60 > do_filp_open+0xb8/0x164 > do_sys_openat2+0x84/0xf0 > __arm64_sys_openat+0x70/0x9c > invoke_syscall+0x58/0x114 > el0_svc_common+0x80/0xe0 > do_el0_svc+0x1c/0x28 > el0_svc+0x38/0x68 > el0t_64_sync_handler+0x68/0xbc > el0t_64_sync+0x1a8/0x1ac > Code: f2fbd5ba eb14013f 540004a1 f940e708 (f9407513) > ---[ end trace 0000000000000000 ]--- > > Suggested-by: Prashanth K <quic_prashk@xxxxxxxxxxx> > Signed-off-by: Lianqin Hu <hulianqin@xxxxxxxx> Include fixes tag and CC stable kernel. > > v2: > - Modify patch content and description according to "v1 suggestion" > - Link to v1: https://lore.kernel.org/all/TYUPR06MB621737D16F68B5ABD6CF5772D2272@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > drivers/usb/gadget/function/u_serial.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c > index 0a8c05b2746b..53d9fc41acc5 100644 > --- a/drivers/usb/gadget/function/u_serial.c > +++ b/drivers/usb/gadget/function/u_serial.c > @@ -579,9 +579,12 @@ static int gs_start_io(struct gs_port *port) > * we didn't in gs_start_tx() */ > tty_wakeup(port->port.tty); > } else { > - gs_free_requests(ep, head, &port->read_allocated); > - gs_free_requests(port->port_usb->in, &port->write_pool, > - &port->write_allocated); > + /* Free reqs only if we are still connected */ > + if (port->port_usb) { > + gs_free_requests(ep, head, &port->read_allocated); > + gs_free_requests(port->port_usb->in, &port->write_pool, > + &port->write_allocated); You can also mention in commit text that skip freeing reqs if port_usb is null, since it will be done by gser_disconnect. Maybe you can wait for other people to review before sending next version. > + } > status = -EIO; > } > Regards, Prashanth K
