On 06/20, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> Add a function fsverity_prepare_setattr() which filesystems that support
> fs-verity must call to deny truncates of verity files.
>
> Reviewed-by: Theodore Ts'o <tytso@xxxxxxx>
Reviewed-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
> fs/verity/open.c | 21 +++++++++++++++++++++
> include/linux/fsverity.h | 7 +++++++
> 2 files changed, 28 insertions(+)
>
> diff --git a/fs/verity/open.c b/fs/verity/open.c
> index 3a3bb27e23f5e3..21ae0ef254a695 100644
> --- a/fs/verity/open.c
> +++ b/fs/verity/open.c
> @@ -296,6 +296,27 @@ int fsverity_file_open(struct inode *inode, struct file *filp)
> }
> EXPORT_SYMBOL_GPL(fsverity_file_open);
>
> +/**
> + * fsverity_prepare_setattr - prepare to change a verity inode's attributes
> + * @dentry: dentry through which the inode is being changed
> + * @attr: attributes to change
> + *
> + * Verity files are immutable, so deny truncates. This isn't covered by the
> + * open-time check because sys_truncate() takes a path, not a file descriptor.
> + *
> + * Return: 0 on success, -errno on failure
> + */
> +int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
> +{
> + if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
> + pr_debug("Denying truncate of verity file (ino %lu)\n",
> + d_inode(dentry)->i_ino);
> + return -EPERM;
> + }
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
> +
> /**
> * fsverity_cleanup_inode - free the inode's verity info, if present
> *
> diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
> index 1372c236c8770c..cbcc358d073652 100644
> --- a/include/linux/fsverity.h
> +++ b/include/linux/fsverity.h
> @@ -46,6 +46,7 @@ static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
> /* open.c */
>
> extern int fsverity_file_open(struct inode *inode, struct file *filp);
> +extern int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
> extern void fsverity_cleanup_inode(struct inode *inode);
>
> #else /* !CONFIG_FS_VERITY */
> @@ -62,6 +63,12 @@ static inline int fsverity_file_open(struct inode *inode, struct file *filp)
> return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
> }
>
> +static inline int fsverity_prepare_setattr(struct dentry *dentry,
> + struct iattr *attr)
> +{
> + return IS_VERITY(d_inode(dentry)) ? -EOPNOTSUPP : 0;
> +}
> +
> static inline void fsverity_cleanup_inode(struct inode *inode)
> {
> }
> --
> 2.22.0.410.gd8fdbe21b5-goog
