[PATCH] nilfs2: fix use-after-free bug in nilfs_mdt_destroy()

[Ryusuke Konishi]

In alloc_inode(), inode_init_always() could return -ENOMEM if
security_inode_alloc() fails.  If this happens for nilfs2,
nilfs_free_inode() is called without initializing inode->i_private and
nilfs_free_inode() wrongly calls nilfs_mdt_destroy(), which frees
uninitialized inode->i_private and can trigger a crash.

Fix this bug by initializing inode->i_private in nilfs_alloc_inode().

Link: https://lkml.kernel.org/r/CAFcO6XOcf1Jj2SeGt=jJV59wmhESeSKpfR0omdFRq+J9nD1vfQ@xxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20211011030956.2459172-1-mudongliangabcd@xxxxxxxxx
Reported-by: butt3rflyh4ck <butterflyhuangxx@xxxxxxxxx>
Reported-by: Hao Sun <sunhao.th@xxxxxxxxx>
Reported-by: Jiacheng Xu <stitch@xxxxxxxxxx>
Reported-by: Mudong Liang <mudongliangabcd@xxxxxxxxx>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
 fs/nilfs2/super.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index ba108f915391..aca5614f1b44 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -159,6 +159,7 @@ struct inode *nilfs_alloc_inode(struct super_block *sb)
 	ii->i_cno = 0;
 	ii->i_assoc_inode = NULL;
 	ii->i_bmap = &ii->i_bmap_data;
+	ii->vfs_inode.i_private = NULL;
 	return &ii->vfs_inode;
 }
 
-- 
2.34.1