5.4-stable review patch. If anyone has any objections, please let me know.
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From: Lianqin Hu hulianqin@vivo.com
commit 4cfbca86f6a8b801f3254e0e3c8f2b1d2d64be2b upstream.
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() 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.
If port_usb is NULL, the release request will be skipped as it will be done by gserial_disconnect.
So add a null pointer check to gs_start_io before attempting to access the value of the pointer port->port_usb.
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
Fixes: c1dca562be8a ("usb gadget: split out serial core") Cc: stable@vger.kernel.org Suggested-by: Prashanth K quic_prashk@quicinc.com Signed-off-by: Lianqin Hu hulianqin@vivo.com Acked-by: Prashanth K quic_prashk@quicinc.com Link: https://lore.kernel.org/r/TYUPR06MB62178DC3473F9E1A537DCD02D2362@TYUPR06MB62... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/function/u_serial.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/drivers/usb/gadget/function/u_serial.c +++ b/drivers/usb/gadget/function/u_serial.c @@ -566,9 +566,12 @@ static int gs_start_io(struct gs_port *p * 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); + } status = -EIO; }