Re: [PATCH] uio: Fix use-after-free in uio_unregister_device()

[Shinichiro Kawasaki]

On Nov 02, 2020 / 13:34, Greg Kroah-Hartman wrote:
> On Mon, Nov 02, 2020 at 09:28:19PM +0900, Shin'ichiro Kawasaki wrote:
> > Commit 8fd0e2a6df26 ("uio: free uio id after uio file node is freed")
> > triggered KASAN use-after-free failure at deletion of TCM-user
> > backstores [1].
> > 
> > In uio_unregister_device(), struct uio_device *idev is passed to
> > uio_free_minor() to refer idev->minor. However, before uio_free_minor()
> > call, idev is already freed by uio_device_release() during call to
> > device_unregister().
> > 
> > To avoid reference to idev->minor after idev free, keep idev->minor
> > value in a local variable. Also modify uio_free_minor() argument to
> > receive the value.
> > 
> > [1]
> > BUG: KASAN: use-after-free in uio_unregister_device+0x166/0x190
> > Read of size 4 at addr ffff888105196508 by task targetcli/49158
> > 
> > CPU: 3 PID: 49158 Comm: targetcli Not tainted 5.10.0-rc1 #1
> > Hardware name: Supermicro Super Server/X10SRL-F, BIOS 2.0 12/17/2015
> > Call Trace:
> >  dump_stack+0xae/0xe5
> >  ? uio_unregister_device+0x166/0x190
> >  print_address_description.constprop.0+0x1c/0x210
> >  ? uio_unregister_device+0x166/0x190
> >  ? uio_unregister_device+0x166/0x190
> >  kasan_report.cold+0x37/0x7c
> >  ? kobject_put+0x80/0x410
> >  ? uio_unregister_device+0x166/0x190
> >  uio_unregister_device+0x166/0x190
> >  tcmu_destroy_device+0x1c4/0x280 [target_core_user]
> >  ? tcmu_release+0x90/0x90 [target_core_user]
> >  ? __mutex_unlock_slowpath+0xd6/0x5d0
> >  target_free_device+0xf3/0x2e0 [target_core_mod]
> >  config_item_cleanup+0xea/0x210
> >  configfs_rmdir+0x651/0x860
> >  ? detach_groups.isra.0+0x380/0x380
> >  vfs_rmdir.part.0+0xec/0x3a0
> >  ? __lookup_hash+0x20/0x150
> >  do_rmdir+0x252/0x320
> >  ? do_file_open_root+0x420/0x420
> >  ? strncpy_from_user+0xbc/0x2f0
> >  ? getname_flags.part.0+0x8e/0x450
> >  do_syscall_64+0x33/0x40
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > RIP: 0033:0x7f9e2bfc91fb
> > Code: 73 01 c3 48 8b 0d 9d ec 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 54 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 6d ec 0c 00 f7 d8 64 89 01 48
> > RSP: 002b:00007ffdd2baafe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
> > RAX: ffffffffffffffda RBX: 00007f9e2beb44a0 RCX: 00007f9e2bfc91fb
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f9e1c20be90
> > RBP: 00007ffdd2bab000 R08: 0000000000000000 R09: 00007f9e2bdf2440
> > R10: 00007ffdd2baaf37 R11: 0000000000000246 R12: 00000000ffffff9c
> > R13: 000055f9abb7e390 R14: 000055f9abcf9558 R15: 00007f9e2be7a780
> > 
> > Allocated by task 34735:
> >  kasan_save_stack+0x1b/0x40
> >  __kasan_kmalloc.constprop.0+0xc2/0xd0
> >  __uio_register_device+0xeb/0xd40
> >  tcmu_configure_device+0x5a0/0xbc0 [target_core_user]
> >  target_configure_device+0x12f/0x760 [target_core_mod]
> >  target_dev_enable_store+0x32/0x50 [target_core_mod]
> >  configfs_write_file+0x2bb/0x450
> >  vfs_write+0x1ce/0x610
> >  ksys_write+0xe9/0x1b0
> >  do_syscall_64+0x33/0x40
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > 
> > Freed by task 49158:
> >  kasan_save_stack+0x1b/0x40
> >  kasan_set_track+0x1c/0x30
> >  kasan_set_free_info+0x1b/0x30
> >  __kasan_slab_free+0x110/0x150
> >  slab_free_freelist_hook+0x5a/0x170
> >  kfree+0xc6/0x560
> >  device_release+0x9b/0x210
> >  kobject_put+0x13e/0x410
> >  uio_unregister_device+0xf9/0x190
> >  tcmu_destroy_device+0x1c4/0x280 [target_core_user]
> >  target_free_device+0xf3/0x2e0 [target_core_mod]
> >  config_item_cleanup+0xea/0x210
> >  configfs_rmdir+0x651/0x860
> >  vfs_rmdir.part.0+0xec/0x3a0
> >  do_rmdir+0x252/0x320
> >  do_syscall_64+0x33/0x40
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > 
> > The buggy address belongs to the object at ffff888105196000
> >  which belongs to the cache kmalloc-2k of size 2048
> > The buggy address is located 1288 bytes inside of
> >  2048-byte region [ffff888105196000, ffff888105196800)
> > The buggy address belongs to the page:
> > page:0000000098e6ca81 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x105190
> > head:0000000098e6ca81 order:3 compound_mapcount:0 compound_pincount:0
> > flags: 0x17ffffc0010200(slab|head)
> > raw: 0017ffffc0010200 dead000000000100 dead000000000122 ffff888100043040
> > raw: 0000000000000000 0000000000080008 00000001ffffffff ffff88810eb55c01
> > page dumped because: kasan: bad access detected
> > page->mem_cgroup:ffff88810eb55c01
> > 
> > Memory state around the buggy address:
> >  ffff888105196400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >  ffff888105196480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > >ffff888105196500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >                       ^
> >  ffff888105196580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >  ffff888105196600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > 
> > Fixes: 8fd0e2a6df26 ("uio: free uio id after uio file node is freed")
> > Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
> > ---
> >  drivers/uio/uio.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> > index 6dca744e39e9..be06f1a961c2 100644
> > --- a/drivers/uio/uio.c
> > +++ b/drivers/uio/uio.c
> > @@ -413,10 +413,10 @@ static int uio_get_minor(struct uio_device *idev)
> >  	return retval;
> >  }
> >  
> > -static void uio_free_minor(struct uio_device *idev)
> > +static void uio_free_minor(unsigned long minor)
> >  {
> >  	mutex_lock(&minor_lock);
> > -	idr_remove(&uio_idr, idev->minor);
> > +	idr_remove(&uio_idr, minor);
> >  	mutex_unlock(&minor_lock);
> >  }
> >  
> > @@ -990,7 +990,7 @@ int __uio_register_device(struct module *owner,
> >  err_uio_dev_add_attributes:
> >  	device_del(&idev->dev);
> >  err_device_create:
> > -	uio_free_minor(idev);
> > +	uio_free_minor(idev->minor);
> >  	put_device(&idev->dev);
> >  	return ret;
> >  }
> > @@ -1042,11 +1042,13 @@ EXPORT_SYMBOL_GPL(__devm_uio_register_device);
> >  void uio_unregister_device(struct uio_info *info)
> >  {
> >  	struct uio_device *idev;
> > +	unsigned long minor;
> >  
> >  	if (!info || !info->uio_dev)
> >  		return;
> >  
> >  	idev = info->uio_dev;
> > +	minor = idev->minor;
> >  
> >  	mutex_lock(&idev->info_lock);
> >  	uio_dev_del_attributes(idev);
> > @@ -1062,7 +1064,7 @@ void uio_unregister_device(struct uio_info *info)
> >  
> >  	device_unregister(&idev->dev);
> >  
> > -	uio_free_minor(idev);
> > +	uio_free_minor(minor);
> 
> Why not just move this call to uio_free_minor() up one line to be above
> device_unregister()?  That should solve this issue and make the change
> much smaller and more obvious.

I thought that the commit 8fd0e2a6df26 intended to move uio_free_minor()
after device_unregister(). Do I misunderstand the intent? If so, I will
simplify the patch as you commented.

-- 
Best Regards,
Shin'ichiro Kawasaki