Re: [PATCH v2] vduse: Fix NULL pointer dereference on sysfs access

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tue, Apr 26, 2022 at 4:07 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, Apr 26, 2022 at 03:36:56PM +0800, Xie Yongji wrote:
> > The control device has no drvdata. So we will get a
> > NULL pointer dereference when accessing control
> > device's msg_timeout attribute via sysfs:
> >
> > [ 132.841881][ T3644] BUG: kernel NULL pointer dereference, address: 00000000000000f8
> > [ 132.850619][ T3644] RIP: 0010:msg_timeout_show (drivers/vdpa/vdpa_user/vduse_dev.c:1271)
> > [ 132.869447][ T3644] dev_attr_show (drivers/base/core.c:2094)
> > [ 132.870215][ T3644] sysfs_kf_seq_show (fs/sysfs/file.c:59)
> > [ 132.871164][ T3644] ? device_remove_bin_file (drivers/base/core.c:2088)
> > [ 132.872082][ T3644] kernfs_seq_show (fs/kernfs/file.c:164)
> > [ 132.872838][ T3644] seq_read_iter (fs/seq_file.c:230)
> > [ 132.873578][ T3644] ? __vmalloc_area_node (mm/vmalloc.c:3041)
> > [ 132.874532][ T3644] kernfs_fop_read_iter (fs/kernfs/file.c:238)
> > [ 132.875513][ T3644] __kernel_read (fs/read_write.c:440 (discriminator 1))
> > [ 132.876319][ T3644] kernel_read (fs/read_write.c:459)
> > [ 132.877129][ T3644] kernel_read_file (fs/kernel_read_file.c:94)
> > [ 132.877978][ T3644] kernel_read_file_from_fd (include/linux/file.h:45 fs/kernel_read_file.c:186)
> > [ 132.879019][ T3644] __do_sys_finit_module (kernel/module.c:4207)
> > [ 132.879930][ T3644] __ia32_sys_finit_module (kernel/module.c:4189)
> > [ 132.880930][ T3644] do_int80_syscall_32 (arch/x86/entry/common.c:112 arch/x86/entry/common.c:132)
> > [ 132.881847][ T3644] entry_INT80_compat (arch/x86/entry/entry_64_compat.S:419)
> >
> > To fix it, don't create the unneeded attribute for
> > control device anymore.
> >
> > Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
> > ---
> >  drivers/vdpa/vdpa_user/vduse_dev.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > index f85d1a08ed87..160e40d03084 100644
> > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > @@ -1344,9 +1344,9 @@ static int vduse_create_dev(struct vduse_dev_config *config,
> >
> >       dev->minor = ret;
> >       dev->msg_timeout = VDUSE_MSG_DEFAULT_TIMEOUT;
> > -     dev->dev = device_create(vduse_class, NULL,
> > -                              MKDEV(MAJOR(vduse_major), dev->minor),
> > -                              dev, "%s", config->name);
> > +     dev->dev = device_create_with_groups(vduse_class, NULL,
> > +                             MKDEV(MAJOR(vduse_major), dev->minor),
> > +                             dev, vduse_dev_groups, "%s", config->name);
> >       if (IS_ERR(dev->dev)) {
> >               ret = PTR_ERR(dev->dev);
> >               goto err_dev;
> > @@ -1595,7 +1595,6 @@ static int vduse_init(void)
> >               return PTR_ERR(vduse_class);
> >
> >       vduse_class->devnode = vduse_devnode;
> > -     vduse_class->dev_groups = vduse_dev_groups;
>
> Ok, this looks much better.
>
> But wow, there are some problems in this code overall.  I see a number
> of flat-out-wrong things in there that should have been caught by code
> reviews.  Some examples:
>         - empty release() callbacks.  That is a huge sign the code
>           design is wrong and broken and you are just trying to make the
>           driver core quiet for some reason.  The documentation in the
>           kernel explains why this is not ok.

Sorry, I failed to find the documentation. Do you mean we should
remove the empty release() callbacks?

>         - __module_get(THIS_MODULE);  That's racy, buggy, and doesn't do
>           what you think it does.  Please never ever ever do that.  It
>           too is a sign of a broken design.

I don't find a good way to remove it. We have to make sure the module
can't be removed until all vduse devices are destroyed.

And I think __module_get(THIS_MODULE) should be safe in our case since
we always call it when we have a reference from open().

>         - no Documentation/ABI/ entries for the sysfs files here.  I
>           think it's burried in some other documentation file but that's
>           not the correct place for it and if you run scripts/get_abi.pl
>           with the code loaded it will rightly complain about this.
>

OK, I will add one.

> Do you want to address these, or do you want patches for them?
>

Let me send some individual patches for them.

Thanks,
Yongji



[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux