linux-kernel - 答复: [PATCH v2] usb: gadget: u_serial: Fix the issue that gs_start

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Message-ID:
 <TYUPR06MB62179BCA9CDFD1125DC8CDEED2232@TYUPR06MB6217.apcprd06.prod.outlook.com>
Date: Fri, 22 Nov 2024 09:18:12 +0000
From: 胡连勤 <hulianqin@...o.com>
To: Prashanth K <quic_prashk@...cinc.com>, "gregkh@...uxfoundation.org"
	<gregkh@...uxfoundation.org>, "quic_jjohnson@...cinc.com"
	<quic_jjohnson@...cinc.com>, "mwalle@...nel.org" <mwalle@...nel.org>
CC: "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	opensource.kernel <opensource.kernel@...o.com>
Subject:
 答复: [PATCH v2] usb: gadget: u_serial: Fix the issue that gs_start_io crashed due to accessing null pointer

Hi Prashanth K:
 
> > 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@...cinc.com>
> > Signed-off-by: Lianqin Hu <hulianqin@...o.com>
> 
> Include fixes tag and CC stable kernel.
> >
> > v2:
> >  - Modify patch content and description according to "v1 suggestion"
> >  - Link to v1:
> > https://apc01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore
> > .kernel.org%2Fall%2FTYUPR06MB621737D16F68B5ABD6CF5772D2272%40TY
> UPR06MB
> >
> 6217.apcprd06.prod.outlook.com%2F&data=05%7C02%7Chulianqin%40vivo.c
> om%
> >
> 7Cd69c2ad2d46d4726186c08dd0acef565%7C923e42dc48d54cbeb5821a797a64
> 12ed%
> >
> 7C0%7C0%7C638678606223680078%7CUnknown%7CTWFpbGZsb3d8eyJFbXB
> 0eU1hcGkiO
> >
> nRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyf
> Q%
> >
> 3D%3D%7C0%7C%7C%7C&sdata=MhFYbqrjUByq%2Fnr4bSYyT4OyXfccCRRoa
> c66zng1G5I
> > %3D&reserved=0
> >
> >  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.

OK, I'll wait for other people's review comments and send a new version later.

> > +		}
> >  		status = -EIO;
> >  	}
> >

Thanks