Re: [PATCH v2 17/25] fs: add vfs_get_fscaps()

Christian Brauner
2024-02-23T08:28:09Z

On Wed, Feb 21, 2024 at 03:24:48PM -0600, Seth Forshee (DigitalOcean) wrote:
> Provide a type-safe interface for retrieving filesystem capabilities and
> a generic implementation suitable for most filesystems. Also add an
> internal interface, vfs_get_fscaps_nosec(), which skips security checks
> for later use from the capability code.
>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> ---
> fs/xattr.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 4 ++++
> 2 files changed, 68 insertions(+)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 06290e4ebc03..10d1b1f78fc2 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -181,6 +181,70 @@ xattr_supports_user_prefix(struct inode *inode)
> }
> EXPORT_SYMBOL(xattr_supports_user_prefix);
>
> +static int generic_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + struct vfs_caps *caps)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct vfs_ns_cap_data nscaps;
> + int ret;
> +
> + ret = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, &nscaps, sizeof(nscaps));
> +
> + if (ret >= 0)
> + ret = vfs_caps_from_xattr(idmap, i_user_ns(inode), caps, &nscaps, ret);
> +
> + return ret;
> +}
> +
> +/**
> + * vfs_get_fscaps_nosec - get filesystem capabilities without security checks
> + * @idmap: idmap of the mount the inode was found from
> + * @dentry: the dentry from which to get filesystem capabilities
> + * @caps: storage in which to return the filesystem capabilities
> + *
> + * This function gets the filesystem capabilities for the dentry and returns
> + * them in @caps. It does not perform security checks.
> + *
> + * Return: 0 on success, a negative errno on error.
> + */
> +int vfs_get_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry,
> + struct vfs_caps *caps)
> +{
> + struct inode *inode = d_inode(dentry);
> +
> + if (inode->i_op->get_fscaps)
> + return inode->i_op->get_fscaps(idmap, dentry, caps);
> + return generic_get_fscaps(idmap, dentry, caps);
> +}
> +
> +/**
> + * vfs_get_fscaps - get filesystem capabilities
> + * @idmap: idmap of the mount the inode was found from
> + * @dentry: the dentry from which to get filesystem capabilities
> + * @caps: storage in which to return the filesystem capabilities
> + *
> + * This function gets the filesystem capabilities for the dentry and returns
> + * them in @caps.
> + *
> + * Return: 0 on success, a negative errno on error.
> + */
> +int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + struct vfs_caps *caps)
> +{
> + int error;
> +
> + /*
> + * The VFS has no restrictions on reading security.* xattrs, so
> + * xattr_permission() isn't needed. Only LSMs get a say.
> + */
> + error = security_inode_get_fscaps(idmap, dentry);
> + if (error)
> + return error;
> +
> + return vfs_get_fscaps_nosec(idmap, dentry, caps);
> +}
> +EXPORT_SYMBOL(vfs_get_fscaps);
> +
> int
> __vfs_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
> struct inode *inode, const char *name, const void *value,
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 89163e0f7aad..d7cd2467e1ea 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2116,6 +2116,10 @@ extern int vfs_dedupe_file_range(struct file *file,
> extern loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
> struct file *dst_file, loff_t dst_pos,
> loff_t len, unsigned int remap_flags);
> +extern int vfs_get_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry,
> + struct vfs_caps *caps);
> +extern int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + struct vfs_caps *caps);

Please drop the externs. Other than my usual complaing about this
falling back to the legacy vfs_*xattr() interfaces,
Reviewed-by: Christian Brauner <brauner@kernel.org>