[PATCH 4.9 018/159] fs: fix UAF/GPF bug in nilfs_mdt_destroy

[Greg Kroah-Hartman]

From: Dongliang Mu <mudongliangabcd@xxxxxxxxx>

commit 2e488f13755ffbb60f307e991b27024716a33b29 upstream.

In alloc_inode, inode_init_always() could return -ENOMEM if
security_inode_alloc() fails, which causes inode->i_private
uninitialized. Then nilfs_is_metadata_file_inode() returns
true and nilfs_free_inode() wrongly calls nilfs_mdt_destroy(),
which frees the uninitialized inode->i_private
and leads to crashes(e.g., UAF/GPF).

Fix this by moving security_inode_alloc just prior to
this_cpu_inc(nr_inodes)

Link: https://lkml.kernel.org/r/CAFcO6XOcf1Jj2SeGt=jJV59wmhESeSKpfR0omdFRq+J9nD1vfQ@xxxxxxxxxxxxxx
Reported-by: butt3rflyh4ck <butterflyhuangxx@xxxxxxxxx>
Reported-by: Hao Sun <sunhao.th@xxxxxxxxx>
Reported-by: Jiacheng Xu <stitch@xxxxxxxxxx>
Reviewed-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/inode.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/fs/inode.c
+++ b/fs/inode.c
@@ -164,8 +164,6 @@ int inode_init_always(struct super_block
 	inode->i_wb_frn_history = 0;
 #endif
 
-	if (security_inode_alloc(inode))
-		goto out;
 	spin_lock_init(&inode->i_lock);
 	lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);
 
@@ -192,11 +190,12 @@ int inode_init_always(struct super_block
 	inode->i_fsnotify_mask = 0;
 #endif
 	inode->i_flctx = NULL;
+
+	if (unlikely(security_inode_alloc(inode)))
+		return -ENOMEM;
 	this_cpu_inc(nr_inodes);
 
 	return 0;
-out:
-	return -ENOMEM;
 }
 EXPORT_SYMBOL(inode_init_always);