On Tue, Apr 26, 2022 at 2:31 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, Apr 26, 2022 at 02:01:03PM +0800, Xie Yongji wrote:
> > The control device has no drvdata. So we will get a NULL
> > NULL pointer dereference when accessing control device's
> > msg_timeout 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, let's add a NULL check in msg_timeout_show() and
> > msg_timeout_store().
> >
> > 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 | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > index f85d1a08ed87..f1c42f4aabb4 100644
> > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > @@ -1268,6 +1268,9 @@ static ssize_t msg_timeout_show(struct device *device,
> > {
> > struct vduse_dev *dev = dev_get_drvdata(device);
> >
> > + if (!dev)
> > + return -EPERM;
> > +
> > return sysfs_emit(buf, "%u\n", dev->msg_timeout);
>
> What prevents the pointer from going away right after you checked it if
> this is something that changes over time?
>
> If this attribute is never going to be valid for this device, just do
> not create it.
>
Got it. Will fix it in v2.
Thanks,
Yongji
