Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open

From: Greg KH
Date: Wed May 13 2020 - 03:04:10 EST

Next message: Manivannan Sadhasivam: "Re: [PATCH v1 3/5] bus: mhi: core: Skip handling BHI irq if MHI reg access is not allowed"
Previous message: Christian KÃnig: "Re: [RFC 09/17] drm/amdgpu: use dma-fence annotations in cs_submit()"
In reply to: rananta: "Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open"
Next in thread: rananta: "Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On Tue, May 12, 2020 at 02:39:50PM -0700, rananta@xxxxxxxxxxxxxx wrote:
> On 2020-05-12 01:25, Greg KH wrote:
> > On Tue, May 12, 2020 at 09:22:15AM +0200, Jiri Slaby wrote:
> > > On 11. 05. 20, 9:39, Greg KH wrote:
> > > > On Mon, May 11, 2020 at 12:23:58AM -0700, rananta@xxxxxxxxxxxxxx wrote:
> > > >> On 2020-05-09 23:48, Greg KH wrote:
> > > >>> On Sat, May 09, 2020 at 06:30:56PM -0700, rananta@xxxxxxxxxxxxxx wrote:
> > > >>>> On 2020-05-06 02:48, Greg KH wrote:
> > > >>>>> On Mon, Apr 27, 2020 at 08:26:01PM -0700, Raghavendra Rao Ananta wrote:
> > > >>>>>> Potentially, hvc_open() can be called in parallel when two tasks calls
> > > >>>>>> open() on /dev/hvcX. In such a scenario, if the
> > > >>>>>> hp->ops->notifier_add()
> > > >>>>>> callback in the function fails, where it sets the tty->driver_data to
> > > >>>>>> NULL, the parallel hvc_open() can see this NULL and cause a memory
> > > >>>>>> abort.
> > > >>>>>> Hence, serialize hvc_open and check if tty->private_data is NULL
> > > >>>>>> before
> > > >>>>>> proceeding ahead.
> > > >>>>>>
> > > >>>>>> The issue can be easily reproduced by launching two tasks
> > > >>>>>> simultaneously
> > > >>>>>> that does nothing but open() and close() on /dev/hvcX.
> > > >>>>>> For example:
> > > >>>>>> $ ./simple_open_close /dev/hvc0 & ./simple_open_close /dev/hvc0 &
> > > >>>>>>
> > > >>>>>> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxxxxxx>
> > > >>>>>> ---
> > > >>>>>> drivers/tty/hvc/hvc_console.c | 16 ++++++++++++++--
> > > >>>>>> 1 file changed, 14 insertions(+), 2 deletions(-)
> > > >>>>>>
> > > >>>>>> diff --git a/drivers/tty/hvc/hvc_console.c
> > > >>>>>> b/drivers/tty/hvc/hvc_console.c
> > > >>>>>> index 436cc51c92c3..ebe26fe5ac09 100644
> > > >>>>>> --- a/drivers/tty/hvc/hvc_console.c
> > > >>>>>> +++ b/drivers/tty/hvc/hvc_console.c
> > > >>>>>> @@ -75,6 +75,8 @@ static LIST_HEAD(hvc_structs);
> > > >>>>>> */
> > > >>>>>> static DEFINE_MUTEX(hvc_structs_mutex);
> > > >>>>>>
> > > >>>>>> +/* Mutex to serialize hvc_open */
> > > >>>>>> +static DEFINE_MUTEX(hvc_open_mutex);
> > > >>>>>> /*
> > > >>>>>> * This value is used to assign a tty->index value to a hvc_struct
> > > >>>>>> based
> > > >>>>>> * upon order of exposure via hvc_probe(), when we can not match it
> > > >>>>>> to
> > > >>>>>> @@ -346,16 +348,24 @@ static int hvc_install(struct tty_driver
> > > >>>>>> *driver, struct tty_struct *tty)
> > > >>>>>> */
> > > >>>>>> static int hvc_open(struct tty_struct *tty, struct file * filp)
> > > >>>>>> {
> > > >>>>>> - struct hvc_struct *hp = tty->driver_data;
> > > >>>>>> + struct hvc_struct *hp;
> > > >>>>>> unsigned long flags;
> > > >>>>>> int rc = 0;
> > > >>>>>>
> > > >>>>>> + mutex_lock(&hvc_open_mutex);
> > > >>>>>> +
> > > >>>>>> + hp = tty->driver_data;
> > > >>>>>> + if (!hp) {
> > > >>>>>> + rc = -EIO;
> > > >>>>>> + goto out;
> > > >>>>>> + }
> > > >>>>>> +
> > > >>>>>> spin_lock_irqsave(&hp->port.lock, flags);
> > > >>>>>> /* Check and then increment for fast path open. */
> > > >>>>>> if (hp->port.count++ > 0) {
> > > >>>>>> spin_unlock_irqrestore(&hp->port.lock, flags);
> > > >>>>>> hvc_kick();
> > > >>>>>> - return 0;
> > > >>>>>> + goto out;
> > > >>>>>> } /* else count == 0 */
> > > >>>>>> spin_unlock_irqrestore(&hp->port.lock, flags);
> > > >>>>>
> > > >>>>> Wait, why isn't this driver just calling tty_port_open() instead of
> > > >>>>> trying to open-code all of this?
> > > >>>>>
> > > >>>>> Keeping a single mutext for open will not protect it from close, it will
> > > >>>>> just slow things down a bit. There should already be a tty lock held by
> > > >>>>> the tty core for open() to keep it from racing things, right?
> > > >>>> The tty lock should have been held, but not likely across
> > > >>>> ->install() and
> > > >>>> ->open() callbacks, thus resulting in a race between hvc_install() and
> > > >>>> hvc_open(),
> > > >>>
> > > >>> How? The tty lock is held in install, and should not conflict with
> > > >>> open(), otherwise, we would be seeing this happen in all tty drivers,
> > > >>> right?
> > > >>>
> > > >> Well, I was expecting the same, but IIRC, I see that the open() was being
> > > >> called in parallel for the same device node.
> > > >
> > > > So open and install are happening at the same time? And the tty_lock()
> > > > does not protect the needed fields from being protected properly? If
> > > > not, what fields are being touched without the lock?
> > > >
> > > >> Is it expected that the tty core would allow only one thread to
> > > >> access the dev-node, while blocking the other, or is it the client
> > > >> driver's responsibility to handle the exclusiveness?
> > > >
> > > > The tty core should handle this correctly, for things that can mess
> > > > stuff up (like install and open at the same time). A driver should not
> > > > have to worry about that.
> > > >
> > > >>>> where hvc_install() sets a data and the hvc_open() clears it.
> > > >>>> hvc_open()
> > > >>>> doesn't
> > > >>>> check if the data was set to NULL and proceeds.
> > > >>>
> > > >>> What data is being set that hvc_open is checking?
> > > >> hvc_install sets tty->private_data to hp, while hvc_open sets it to NULL (in
> > > >> one of the paths).
> > > >
> > > > I see no use of private_data in drivers/tty/hvc/ so what exactly are you
> > > > referring to?
> > >
> > > He likely means tty->driver_data. And there exactly lays the issue.
> > >
> > > commit bdb498c20040616e94b05c31a0ceb3e134b7e829
> > > Author: Jiri Slaby <jslaby@xxxxxxx>
> > > Date: Tue Aug 7 21:48:04 2012 +0200
> > >
> > > TTY: hvc_console, add tty install
> > >
> > > added hvc_install but did not move 'tty->driver_data = NULL;' from
> > > hvc_open's fail path to hvc_cleanup.
> > >
> > > IOW hvc_open now NULLs tty->driver_data even for another task which
> > > opened the tty earlier. The same holds for
> > > "tty_port_tty_set(&hp->port,
> > > NULL);" there. And actually "tty_port_put(&hp->port);" is also
> > > incorrect
> > > for the 2nd task opening the tty.
> > >
> > > So, a mutex with tty->driver_data check in open is not definitely the
> > > way to go. This mess needs to be sorted out properly. Sure, a good
> > > start
> > > would be a conversion to tty_port_open. Right after dropping "tty:
> > > hvc:
> > > Fix data abort due to race in hvc_open" from tty/tty-next :).
> >
> > I've now reverted this commit so we can start from a "clean" place.
> >
> > > What I *don't* understand is why hp->ops->notifier_add fails, given
> > > the
> > > open does not allow multiple opens anyway?
> >
> > I don't understand that either. Raghavendra, can you show a real trace
> > for this issue that shows this?
> >
> Let me know if this helps:
>
> [ 265.332900] Unable to handle kernel NULL pointer dereference at virtual
> address 00000000000000a8
> [ 265.332920] Mem abort info:
> [ 265.332934] ESR = 0x96000006
> [ 265.332950] EC = 0x25: DABT (current EL), IL = 32 bits
> [ 265.332963] SET = 0, FnV = 0
> [ 265.332975] EA = 0, S1PTW = 0
> [ 265.332985] Data abort info:
> [ 265.332997] ISV = 0, ISS = 0x00000006
> [ 265.333008] CM = 0, WnR = 0
> [ 265.333025] user pgtable: 4k pages, 39-bit VAs, pgdp=00000001620f3000
> [ 265.333038] [00000000000000a8] pgd=00000001620f2003,
> pud=00000001620f2003, pmd=0000000000000000
> [ 265.333071] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> [ 265.333424] CPU: 1 PID: 5653 Comm: stress-ng-dev Tainted: G S W O
> 5.4.12-g04866e0 #1
> [ 265.333458] pstate: 80400085 (Nzcv daIf +PAN -UAO)
> [ 265.333499] pc : _raw_spin_lock_irqsave+0x40/0x7c
> [ 265.333517] lr : _raw_spin_lock_irqsave+0x38/0x7c
> [ 265.333530] sp : ffffffc02436ba40
> [ 265.333542] x29: ffffffc02436ba40 x28: 0000000000020800
> [ 265.333562] x27: ffffffdfb4046490 x26: ffffff8101b83400
> [ 265.333580] x25: ffffff80e163ad00 x24: ffffffdfb45c7798
> [ 265.333598] x23: ffffff8101b83668 x22: ffffffdfb4974000
> [ 265.333617] x21: 0000000000000001 x20: 00000000000000a8
> [ 265.333634] x19: 0000000000000000 x18: ffffff80e0b0d460
> [ 265.333652] x17: 0000000000000000 x16: 0000000001000000
> [ 265.333670] x15: 0000000001000000 x14: 00000000f8000000
> [ 265.333688] x13: 0000000000000000 x12: 0000000000000001
> [ 265.333706] x11: 17f5f16765f64600 x10: 17f5f16765f64600
> [ 265.333724] x9 : ffffffdfb3444244 x8 : 0000000000000000
> [ 265.333741] x7 : 0000000000000000 x6 : 0000000000000000
> [ 265.333759] x5 : 0000000000000000 x4 : 0000000000000002
> [ 265.333776] x3 : ffffffc02436b9c0 x2 : ffffffdfb40456e0
> [ 265.333794] x1 : ffffffc02436b9c0 x0 : ffffffdfb3444244
> [ 265.333812] Call trace:
> [ 265.333831] _raw_spin_lock_irqsave+0x40/0x7c
> [ 265.333859] hvc_open$61deaf328f140fd7df47c115ec866fa5+0x28/0x174
> [ 265.333882] tty_open$86bd494905ebe22944bf63b711173de3+0x3d0/0x584
> [ 265.333921] chrdev_open$4083aaa799bca8e0e1e0c8dc1947aa96+0x1c4/0x248
> [ 265.333940] do_dentry_open+0x258/0x3b0
> [ 265.333956] vfs_open+0x2c/0x38
> [ 265.333975] path_openat+0x898/0xedc
> [ 265.333991] do_filp_open+0x78/0x124
> [ 265.334006] do_sys_open+0x13c/0x298
> [ 265.334022] __arm64_sys_openat+0x28/0x34
> [ 265.334044] el0_svc_common+0xb8/0x1b4
> [ 265.334059] el0_svc_handler+0x6c/0x88
> [ 265.334079] el0_svc+0x8/0xc
> [ 265.334110] Code: 52800035 97b9fec7 aa1f03e8 f9800291 (885ffe81)
> [ 265.334130] ---[ end trace ac90e3099a98e99f ]---
> [ 265.334146] Kernel panic - not syncing: Fatal exception

Hm, do you have a strace showing the close happening at the same time?
What about install()?

And what line in hvc_open() does that offset correspond to?

thanks,

greg k-h

Next message: Manivannan Sadhasivam: "Re: [PATCH v1 3/5] bus: mhi: core: Skip handling BHI irq if MHI reg access is not allowed"
Previous message: Christian KÃnig: "Re: [RFC 09/17] drm/amdgpu: use dma-fence annotations in cs_submit()"
In reply to: rananta: "Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open"
Next in thread: rananta: "Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]