linux-hardening - Re: [PATCH 5/5] pstore: inode: Use cleanup.h for struct pstore

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Date: Sat, 2 Dec 2023 22:27:06 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Kees Cook <keescook@...omium.org>
Cc: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Tony Luck <tony.luck@...el.com>, linux-hardening@...r.kernel.org,
	Christian Brauner <brauner@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 5/5] pstore: inode: Use cleanup.h for struct
 pstore_private

On Sat, Dec 02, 2023 at 01:22:15PM -0800, Kees Cook wrote:

>  static void *pstore_ftrace_seq_start(struct seq_file *s, loff_t *pos)
>  {
> @@ -338,9 +339,8 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
>  {
>  	struct dentry		*dentry;
>  	struct inode		*inode __free(iput) = NULL;
> -	int			rc = 0;
>  	char			name[PSTORE_NAMELEN];
> -	struct pstore_private	*private, *pos;
> +	struct pstore_private	*private __free(pstore_private) = NULL, *pos;
>  	size_t			size = record->size + record->ecc_notice_size;
>  
>  	if (WARN_ON(!inode_is_locked(d_inode(root))))
> @@ -356,7 +356,6 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
>  			return -EEXIST;
>  	}
>  
> -	rc = -ENOMEM;
>  	inode = pstore_get_inode(root->d_sb);
>  	if (!inode)
>  		return -ENOMEM;
> @@ -373,7 +372,7 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
>  
>  	dentry = d_alloc_name(root, name);
>  	if (!dentry)
> -		goto fail_private;
> +		return -ENOMEM;
>  
>  	private->dentry = dentry;
>  	private->record = record;
> @@ -386,13 +385,9 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
>  
>  	d_add(dentry, no_free_ptr(inode));
>  
> -	list_add(&private->list, &records_list);
> +	list_add(&(no_free_ptr(private))->list, &records_list);

That's really brittle.  It critically depends upon having no failure
exits past the assignment to ->i_private; once you've done that,
you have transferred the ownership of that thing to the inode
(look at your ->evict_inode()).  But you can't say
        inode->i_private = no_free_ptr(private);
since you are using private past that point.