Patch "drm: fix null-ptr-deref in drm_dev_init_release()" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    drm: fix null-ptr-deref in drm_dev_init_release()

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-fix-null-ptr-deref-in-drm_dev_init_release.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8c889b389c6e2c5a0ce5aac21a10ac08a3d7d935
Author: Wang Hai <wanghai38@xxxxxxxxxx>
Date:   Wed Oct 13 19:41:39 2021 +0800

    drm: fix null-ptr-deref in drm_dev_init_release()
    
    [ Upstream commit acf20ed020ffa4d6cc8347e8d356509b95df3cbe ]
    
    I got a null-ptr-deref report:
    
    [drm:drm_dev_init [drm]] *ERROR* Cannot allocate anonymous inode: -12
    ==================================================================
    BUG: KASAN: null-ptr-deref in iput+0x3c/0x4a0
    ...
    Call Trace:
     dump_stack_lvl+0x6c/0x8b
     kasan_report.cold+0x64/0xdb
     __asan_load8+0x69/0x90
     iput+0x3c/0x4a0
     drm_dev_init_release+0x39/0xb0 [drm]
     drm_managed_release+0x158/0x2d0 [drm]
     drm_dev_init+0x3a7/0x4c0 [drm]
     __devm_drm_dev_alloc+0x55/0xd0 [drm]
     mi0283qt_probe+0x8a/0x2b5 [mi0283qt]
     spi_probe+0xeb/0x130
    ...
     entry_SYSCALL_64_after_hwframe+0x44/0xae
    
    If drm_fs_inode_new() fails in drm_dev_init(), dev->anon_inode will point
    to PTR_ERR(...) instead of NULL. This will result in null-ptr-deref when
    drm_fs_inode_free(dev->anon_inode) is called.
    
    drm_dev_init()
            drm_fs_inode_new() // fail, dev->anon_inode = PTR_ERR(...)
            drm_managed_release()
                    drm_dev_init_release()
                            drm_fs_inode_free() // access non-existent anon_inode
    
    Define a temp variable and assign it to dev->anon_inode if the temp
    variable is not PTR_ERR.
    
    Fixes: 2cbf7fc6718b ("drm: Use drmm_ for drm_dev_init cleanup")
    Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
    Signed-off-by: Wang Hai <wanghai38@xxxxxxxxxx>
    Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx>
    Link: https://patchwork.freedesktop.org/patch/msgid/20211013114139.4042207-1-wanghai38@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index cd162d406078a..006e3b896caea 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -577,6 +577,7 @@ static int drm_dev_init(struct drm_device *dev,
 			struct drm_driver *driver,
 			struct device *parent)
 {
+	struct inode *inode;
 	int ret;
 
 	if (!drm_core_init_complete) {
@@ -613,13 +614,15 @@ static int drm_dev_init(struct drm_device *dev,
 	if (ret)
 		return ret;
 
-	dev->anon_inode = drm_fs_inode_new();
-	if (IS_ERR(dev->anon_inode)) {
-		ret = PTR_ERR(dev->anon_inode);
+	inode = drm_fs_inode_new();
+	if (IS_ERR(inode)) {
+		ret = PTR_ERR(inode);
 		DRM_ERROR("Cannot allocate anonymous inode: %d\n", ret);
 		goto err;
 	}
 
+	dev->anon_inode = inode;
+
 	if (drm_core_check_feature(dev, DRIVER_RENDER)) {
 		ret = drm_minor_alloc(dev, DRM_MINOR_RENDER);
 		if (ret)