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Wed, 18 Aug 2021 22:31:57 -0700 (PDT) From: Desmond Cheong Zhi Xi To: Daniel Vetter Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Dave Airlie , Sumit Semwal , =?UTF-8?Q?Christian_K=c3=b6nig?= , Jens Axboe , Oleg Nesterov , Thomas Gleixner , Dmitry Vyukov , walter-zh.wu@mediatek.com, dri-devel , Linux Kernel Mailing List , intel-gfx , "open list:DMA BUFFER SHARING FRAMEWORK" , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Shuah Khan , Greg KH , linux-kernel-mentees@lists.linuxfoundation.org References: <20210818073824.1560124-1-desmondcheongzx@gmail.com> <20210818073824.1560124-5-desmondcheongzx@gmail.com> <53a63ac8-f2de-91f7-4e0f-20b0f3f61d52@gmail.com> Message-ID: <18df91cb-3948-f4f4-d548-8d23107540ae@gmail.com> Date: Thu, 19 Aug 2021 13:31:51 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Intel-gfx] [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth, ioctl} X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 19/8/21 12:33 am, Daniel Vetter wrote: > On Wed, Aug 18, 2021 at 5:37 PM Desmond Cheong Zhi Xi > wrote: >> >> On 18/8/21 6:11 pm, Daniel Vetter wrote: >>> On Wed, Aug 18, 2021 at 03:38:19PM +0800, Desmond Cheong Zhi Xi wrote: >>>> There are three areas where we dereference struct drm_master without >>>> checking if the pointer is non-NULL. >>>> >>>> 1. drm_getmagic is called from the ioctl_handler. Since >>>> DRM_IOCTL_GET_MAGIC has no ioctl flags, drm_getmagic is run without >>>> any check that drm_file.master has been set. >>>> >>>> 2. Similarly, drm_getunique is called from the ioctl_handler, but >>>> DRM_IOCTL_GET_UNIQUE has no ioctl flags. So there is no guarantee that >>>> drm_file.master has been set. >>> >>> I think the above two are impossible, due to the refcounting rules for >>> struct file. >>> >> >> Right, will drop those two parts from the patch. >> >>>> 3. drm_master_release can also be called without having a >>>> drm_file.master set. Here is one error path: >>>> drm_open(): >>>> drm_open_helper(): >>>> drm_master_open(): >>>> drm_new_set_master(); <--- returns -ENOMEM, >>>> drm_file.master not set >>>> drm_file_free(): >>>> drm_master_release(); <--- NULL ptr dereference >>>> (file_priv->master->magic_map) >>>> >>>> Fix these by checking if the master pointers are NULL before use. >>>> >>>> Signed-off-by: Desmond Cheong Zhi Xi >>>> --- >>>> drivers/gpu/drm/drm_auth.c | 16 ++++++++++++++-- >>>> drivers/gpu/drm/drm_ioctl.c | 5 +++++ >>>> 2 files changed, 19 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c >>>> index f9267b21556e..b7230604496b 100644 >>>> --- a/drivers/gpu/drm/drm_auth.c >>>> +++ b/drivers/gpu/drm/drm_auth.c >>>> @@ -95,11 +95,18 @@ EXPORT_SYMBOL(drm_is_current_master); >>>> int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) >>>> { >>>> struct drm_auth *auth = data; >>>> + struct drm_master *master; >>>> int ret = 0; >>>> >>>> mutex_lock(&dev->master_mutex); >>>> + master = file_priv->master; >>>> + if (!master) { >>>> + mutex_unlock(&dev->master_mutex); >>>> + return -EINVAL; >>>> + } >>>> + >>>> if (!file_priv->magic) { >>>> - ret = idr_alloc(&file_priv->master->magic_map, file_priv, >>>> + ret = idr_alloc(&master->magic_map, file_priv, >>>> 1, 0, GFP_KERNEL); >>>> if (ret >= 0) >>>> file_priv->magic = ret; >>>> @@ -355,8 +362,12 @@ void drm_master_release(struct drm_file *file_priv) >>>> >>>> mutex_lock(&dev->master_mutex); >>>> master = file_priv->master; >>>> + >>>> + if (!master) >>>> + goto unlock; >>> >>> This is a bit convoluted, since we're in the single-threaded release path >>> we don't need any locking for file_priv related things. Therefore we can >>> pull the master check out and just directly return. >>> >>> But since it's a bit surprising maybe a comment that this can happen when >>> drm_master_open in drm_open_helper fails? >>> >> >> Sounds good. This can actually also happen in the failure path of >> mock_drm_getfile if anon_inode_getfile fails. I'll leave a short note >> about both of them. >> >>> Another option, and maybe cleaner, would be to move the drm_master_release >>> from drm_file_free into drm_close_helper. That would be fully symmetrical >>> and should also fix the bug here? >>> -Daniel >>> >> Hmmm maybe the first option to move the check out of the lock might be >> better. If I'm not wrong, we would otherwise also need to move >> drm_master_release into drm_client_close. > > Do we have to? > > If I haven't missed anything, the drm_client stuff only calls > drm_file_alloc and doesn't set up a master. So this should work? > -Daniel > Ahhhh ok yes, I understand what's going on better now. I think you're right, moving drm_master_release into drm_close_helper should fix all the places it can go wrong. >> >>> >>>> + >>>> if (file_priv->magic) >>>> - idr_remove(&file_priv->master->magic_map, file_priv->magic); >>>> + idr_remove(&master->magic_map, file_priv->magic); >>>> >>>> if (!drm_is_current_master_locked(file_priv)) >>>> goto out; >>>> @@ -379,6 +390,7 @@ void drm_master_release(struct drm_file *file_priv) >>>> drm_master_put(&file_priv->master); >>>> spin_unlock(&dev->master_lookup_lock); >>>> } >>>> +unlock: >>>> mutex_unlock(&dev->master_mutex); >>>> } >>>> >>>> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c >>>> index 26f3a9ede8fe..4d029d3061d9 100644 >>>> --- a/drivers/gpu/drm/drm_ioctl.c >>>> +++ b/drivers/gpu/drm/drm_ioctl.c >>>> @@ -121,6 +121,11 @@ int drm_getunique(struct drm_device *dev, void *data, >>>> >>>> mutex_lock(&dev->master_mutex); >>>> master = file_priv->master; >>>> + if (!master) { >>>> + mutex_unlock(&dev->master_mutex); >>>> + return -EINVAL; >>>> + } >>>> + >>>> if (u->unique_len >= master->unique_len) { >>>> if (copy_to_user(u->unique, master->unique, master->unique_len)) { >>>> mutex_unlock(&dev->master_mutex); >>>> -- >>>> 2.25.1 >>>> >>> >> > >