linux-kernel - [PATCH] fs: fix GPF in nilfs_mdt

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Date:   Mon, 11 Oct 2021 11:09:56 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Dongliang Mu <mudongliangabcd@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs: fix GPF in nilfs_mdt_destroy

In alloc_inode, inode_init_always could return -NOMEM if
security_inode_alloc fails. In its error handling, i_callback and
nilfs_free_inode will be called. However, because inode->i_private is
not initialized due to the failure of security_inode_alloc, the function
nilfs_is_metadata_file_inode can return true and nilfs_mdt_destroy will
be executed to lead to GPF bug.

Fix this bug by moving the assignment of inode->i_private before
security_inode_alloc.

BTW, this bug is triggered by fault injection in the syzkaller.

Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
---
 fs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index ed0cab8a32db..f6fce84bf550 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -160,6 +160,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	inode->i_dir_seq = 0;
 	inode->i_rdev = 0;
 	inode->dirtied_when = 0;
+	inode->i_private = NULL;

 #ifdef CONFIG_CGROUP_WRITEBACK
 	inode->i_wb_frn_winner = 0;
@@ -194,7 +195,6 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	lockdep_set_class_and_name(&mapping->invalidate_lock,
 				   &sb->s_type->invalidate_lock_key,
 				   "mapping.invalidate_lock");
-	inode->i_private = NULL;
 	inode->i_mapping = mapping;
 	INIT_HLIST_HEAD(&inode->i_dentry);	/* buggered by rcu freeing */
 #ifdef CONFIG_FS_POSIX_ACL
-- 
2.25.1