fs: fix UAF/GPF bug in nilfs_mdt_destroy

JIRA: https://issues.redhat.com/browse/RHEL-116661
CVE: CVE-2022-50367

commit 2e488f1
Author: Dongliang Mu <mudongliangabcd@gmail.com>
Date:   Tue Aug 16 12:08:58 2022 +0800

    fs: fix UAF/GPF bug in nilfs_mdt_destroy

    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@mail.gmail.com
    Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
    Reported-by: Hao Sun <sunhao.th@gmail.com>
    Reported-by: Jiacheng Xu <stitch@zju.edu.cn>
    Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
    Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: stable@vger.kernel.org
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

fs/inode.c

@@ -193,8 +193,6 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	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);
 
@@ -231,11 +229,12 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	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);