[PATCH] drm/radeon: fix race condition UAF in radeon_gem_set_domain_ioctl

[kernel test robot]

Hi Min,

kernel test robot noticed the following build warnings:

[auto build test WARNING on drm-misc/drm-misc-next]
[also build test WARNING on linus/master v6.4-rc3 next-20230525]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Min-Li/drm-radeon-fix-race-condition-UAF-in-radeon_gem_set_domain_ioctl/20230527-155623
base:   git://anongit.freedesktop.org/drm/drm-misc drm-misc-next
patch link:    https://lore.kernel.org/r/20230526123753.16160-1-lm0963hack%40gmail.com
patch subject: [PATCH] drm/radeon: fix race condition UAF in radeon_gem_set_domain_ioctl
config: mips-allyesconfig (https://download.01.org/0day-ci/archive/20230527/202305271806.VvOClWyB-lkp@intel.com/config)
compiler: mips-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        mkdir -p ~/bin
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/66fb975494d21e80b90235b7d8bf0953990c5c89
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Min-Li/drm-radeon-fix-race-condition-UAF-in-radeon_gem_set_domain_ioctl/20230527-155623
        git checkout 66fb975494d21e80b90235b7d8bf0953990c5c89
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 ~/bin/make.cross W=1 O=build_dir ARCH=mips olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 ~/bin/make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash drivers/gpu/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp at intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202305271806.VvOClWyB-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/gpu/drm/radeon/radeon_gem.c: In function 'radeon_gem_set_domain_ioctl':
>> drivers/gpu/drm/radeon/radeon_gem.c:462:27: warning: variable 'robj' set but not used [-Wunused-but-set-variable]
     462 |         struct radeon_bo *robj;
         |                           ^~~~


vim +/robj +462 drivers/gpu/drm/radeon/radeon_gem.c

f72a113a71ab08 Christian König 2014-08-07  453  
771fe6b912fca5 Jerome Glisse   2009-06-05  454  int radeon_gem_set_domain_ioctl(struct drm_device *dev, void *data,
771fe6b912fca5 Jerome Glisse   2009-06-05  455  				struct drm_file *filp)
771fe6b912fca5 Jerome Glisse   2009-06-05  456  {
771fe6b912fca5 Jerome Glisse   2009-06-05  457  	/* transition the BO to a domain -
771fe6b912fca5 Jerome Glisse   2009-06-05  458  	 * just validate the BO into a certain domain */
dee53e7fb3ee01 Jerome Glisse   2012-07-02  459  	struct radeon_device *rdev = dev->dev_private;
771fe6b912fca5 Jerome Glisse   2009-06-05  460  	struct drm_radeon_gem_set_domain *args = data;
771fe6b912fca5 Jerome Glisse   2009-06-05  461  	struct drm_gem_object *gobj;
4c7886791264f0 Jerome Glisse   2009-11-20 @462  	struct radeon_bo *robj;
771fe6b912fca5 Jerome Glisse   2009-06-05  463  	int r;
771fe6b912fca5 Jerome Glisse   2009-06-05  464  
771fe6b912fca5 Jerome Glisse   2009-06-05  465  	/* for now if someone requests domain CPU -
771fe6b912fca5 Jerome Glisse   2009-06-05  466  	 * just make sure the buffer is finished with */
dee53e7fb3ee01 Jerome Glisse   2012-07-02  467  	down_read(&rdev->exclusive_lock);
771fe6b912fca5 Jerome Glisse   2009-06-05  468  
771fe6b912fca5 Jerome Glisse   2009-06-05  469  	/* just do a BO wait for now */
a8ad0bd84f9860 Chris Wilson    2016-05-09  470  	gobj = drm_gem_object_lookup(filp, args->handle);
771fe6b912fca5 Jerome Glisse   2009-06-05  471  	if (gobj == NULL) {
dee53e7fb3ee01 Jerome Glisse   2012-07-02  472  		up_read(&rdev->exclusive_lock);
bf79cb914dbfe8 Chris Wilson    2010-08-04  473  		return -ENOENT;
771fe6b912fca5 Jerome Glisse   2009-06-05  474  	}
7e4d15d90afe46 Daniel Vetter   2011-02-18  475  	robj = gem_to_radeon_bo(gobj);
771fe6b912fca5 Jerome Glisse   2009-06-05  476  
771fe6b912fca5 Jerome Glisse   2009-06-05  477  	r = radeon_gem_set_domain(gobj, args->read_domains, args->write_domain);
771fe6b912fca5 Jerome Glisse   2009-06-05  478  
f11fb66ae92193 Emil Velikov    2020-05-15  479  	drm_gem_object_put(gobj);
dee53e7fb3ee01 Jerome Glisse   2012-07-02  480  	up_read(&rdev->exclusive_lock);
66fb975494d21e Min Li          2023-05-26  481  	r = radeon_gem_handle_lockup(rdev, r);
771fe6b912fca5 Jerome Glisse   2009-06-05  482  	return r;
771fe6b912fca5 Jerome Glisse   2009-06-05  483  }
771fe6b912fca5 Jerome Glisse   2009-06-05  484  

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