linux-kernel - Re: [PATCH 01/29] xattr: make the xattr array itself const

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Date:   Mon, 2 Oct 2023 11:58:18 +0200
From:   Thomas Weißschuh <linux@...ssschuh.net>
To:     Wedson Almeida Filho <wedsonaf@...il.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <walmeida@...rosoft.com>
Subject: Re: [PATCH 01/29] xattr: make the xattr array itself const

On 2023-09-30 02:00:05-0300, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@...rosoft.com>
> 
> As it is currently declared, the xattr_handler structs are const but the
> array containing their pointers is not. This patch makes it so that fs
> modules can place them in .rodata, which makes it harder for
> accidental/malicious modifications at runtime.

You could also add an entry to scripts/const_structs.checkpatch to make
sure newly introduced usages of the struct are const.

Could be a single dedicated patch after this patch has been applied.

> Signed-off-by: Wedson Almeida Filho <walmeida@...rosoft.com>
> ---
>  fs/xattr.c         | 6 +++---
>  include/linux/fs.h | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index e7bbb7f57557..1905f8ede13d 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -56,7 +56,7 @@ strcmp_prefix(const char *a, const char *a_prefix)
>  static const struct xattr_handler *
>  xattr_resolve_name(struct inode *inode, const char **name)
>  {
> -	const struct xattr_handler **handlers = inode->i_sb->s_xattr;
> +	const struct xattr_handler * const *handlers = inode->i_sb->s_xattr;
>  	const struct xattr_handler *handler;
>  
>  	if (!(inode->i_opflags & IOP_XATTR)) {
> @@ -162,7 +162,7 @@ xattr_permission(struct mnt_idmap *idmap, struct inode *inode,
>  int
>  xattr_supports_user_prefix(struct inode *inode)
>  {
> -	const struct xattr_handler **handlers = inode->i_sb->s_xattr;
> +	const struct xattr_handler * const *handlers = inode->i_sb->s_xattr;
>  	const struct xattr_handler *handler;
>  
>  	if (!(inode->i_opflags & IOP_XATTR)) {
> @@ -999,7 +999,7 @@ int xattr_list_one(char **buffer, ssize_t *remaining_size, const char *name)
>  ssize_t
>  generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
>  {
> -	const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
> +	const struct xattr_handler *handler, * const *handlers = dentry->d_sb->s_xattr;
>  	ssize_t remaining_size = buffer_size;
>  	int err = 0;
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 562f2623c9c9..4d8003f48216 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1172,7 +1172,7 @@ struct super_block {
>  #ifdef CONFIG_SECURITY
>  	void                    *s_security;
>  #endif
> -	const struct xattr_handler **s_xattr;
> +	const struct xattr_handler * const *s_xattr;
>  #ifdef CONFIG_FS_ENCRYPTION
>  	const struct fscrypt_operations	*s_cop;
>  	struct fscrypt_keyring	*s_master_keys; /* master crypto keys in use */
> -- 
> 2.34.1
>