linux-kernel - [PATCH] fs/inode.c: change the order of initialization in inode_init

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Date:   Sat, 27 Aug 2022 17:09:26 +0300
From:   Alexey Khoroshilov <khoroshilov@...ras.ru>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Rustam Subkhankulov <subkhankulov@...ras.ru>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        ldv-project@...uxtesting.org
Subject: [PATCH] fs/inode.c: change the order of initialization in inode_init_always()

From: Rustam Subkhankulov <subkhankulov@...ras.ru>

If function 'security_inode_alloc()' returns a nonzero value at
[fs/inode.c: 195] due to an error (e.g. fail to allocate memory),
then some of the fields, including 'i_private', will not be
initialized.

After that, if the fs-specfic free_inode function is called in
'i_callback', the nonzero value of 'i_private' field can be interpreted
as initialized. As a result, this can cause dereferencing of random
value pointer (e.g. nilfs2).

In earlier versions, a similar situation could occur with the 'u' union
in 'inode' structure.

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

Signed-off-by: Rustam Subkhankulov <subkhankulov@...ras.ru>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
---
 fs/inode.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index bd4da9c5207e..08d093737e8c 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -192,8 +192,6 @@ 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);

@@ -230,9 +228,10 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	inode->i_flctx = NULL;
 	this_cpu_inc(nr_inodes);

+	if (security_inode_alloc(inode))
+		return -ENOMEM;
+
 	return 0;
-out:
-	return -ENOMEM;
 }
 EXPORT_SYMBOL(inode_init_always);

-- 
2.34.1