Greg KH
2022-Apr-26 13:34 UTC
[PATCH v2] vduse: Fix NULL pointer dereference on sysfs access
On Tue, Apr 26, 2022 at 09:17:23PM +0800, Yongji Xie wrote:> On Tue, Apr 26, 2022 at 8:44 PM Greg KH <gregkh at linuxfoundation.org> wrote: > > > > On Tue, Apr 26, 2022 at 08:30:38PM +0800, Yongji Xie wrote: > > > On Tue, Apr 26, 2022 at 6:26 PM Greg KH <gregkh at linuxfoundation.org> wrote: > > > > > > > > On Tue, Apr 26, 2022 at 05:41:15PM +0800, Yongji Xie wrote: > > > > > On Tue, Apr 26, 2022 at 4:07 PM Greg KH <gregkh at linuxfoundation.org> 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 at intel.com> > > > > > > > Cc: stable at vger.kernel.org > > > > > > > Signed-off-by: Xie Yongji <xieyongji at bytedance.com> > > > > > > > --- > > > > > > > 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? > > > > > > > > Yes, why are they needed? > > > > > > > > (hint, retorical question, you added them to remove the driver core > > > > warning when the device is removed, which means someone added them just > > > > because they thought that their code could ignore the hints that the > > > > driver core was telling them.) > > > > > > > > > > OK, I see. > > > > > > > Please properly free the memory here. > > > > > > > > > > One question is how to deal with the case if the device/kobject is > > > defined as a static variable. We should not need to free any resources > > > in this case. Or do you suggest just using dynamic allocation here? > > > > A kobject can NEVER be a static variable[1]. That's not how the driver > > model works at all. If this is how this code is written, it needs to be > > fixed. > > > > OK, I see. > > > [1] Ok, yes, drivers and busses and classes have static kobjects, ignore > > them... > > > > > > > > > > > - __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. > > > > > > > > That will happen automatically when the module is removed. > > > > > > > > > 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(). > > > > > > > > What happened if someone removed the module _right before_ this was > > > > called? You can not grab your own reference count safely. > > > > > > > > > > I don't get you here. We should already grab a reference count from > > > open() before calling this. So it should fail if someone tries to > > > remove the module at this time. > > > > Then why are you trying to grab the module reference again? > > > > > > Please just remove it, it's not needed and is broken. There should not > > > > be any reason that the module can not be unloaded, UNLESS a file handle > > > > is open, and you properly handle that already. > > > > > > > > > > But in our case, I think we should prevent unloading the module If we > > > already created some vduse devices via /dev/vduse/control (note that > > > the control device's file handle could be closed after device > > > creation). Otherwise, we might get some crashes when accessing those > > > created vduse devices. > > > > Then the code is written incorrectly, this should not be an issue at > > all. Your devices will all be cleaned up properly before your code is > > unloaded from the system. > > > > In current design, the vduse device can't be cleaned up properly until > it is unbinded from the vDPA bus explicitly. So I use the extra > __module_get() to make sure we can't unload the module until the > device is cleaned up properly.Then something is wrong, it should not work that way.> > Note that no other driver or bus does this, what makes this different? > > > > I can see some similar behavior in loop and rbd modules.Never treat the loop code as a good example :) This should not be needed, when your module is unloaded, all devices it handled should be properly removed by it. thanks, greg k-h