Re: [PATCH v2 19/25] fs: add vfs_remove_fscaps()

Christian Brauner
2024-02-23T08:40:13Z

On Wed, Feb 21, 2024 at 03:24:50PM -0600, Seth Forshee (DigitalOcean) wrote:
> Provide a type-safe interface for removing filesystem capabilities and a
> generic implementation suitable for most filesystems. Also add an
> internal interface, vfs_remove_fscaps_nosec(), which is called with the
> inode lock held and skips security checks for later use from the
> capability code.
>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> ---
> fs/xattr.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 2 files changed, 83 insertions(+)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 96de43928a51..8b0f7384cbc9 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -324,6 +324,87 @@ int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> }
> EXPORT_SYMBOL(vfs_set_fscaps);
>
> +static int generic_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry)
> +{
> + return __vfs_removexattr(idmap, dentry, XATTR_NAME_CAPS);
> +}
> +
> +/**
> + * vfs_remove_fscaps_nosec - remove filesystem capabilities without
> + * security checks
> + * @idmap: idmap of the mount the inode was found from
> + * @dentry: the dentry from which to remove filesystem capabilities
> + *
> + * This function removes any filesystem capabilities from the specified
> + * dentry. Does not perform any security checks, and callers must hold the
> + * inode lock.
> + *
> + * Return: 0 on success, a negative errno on error.
> + */
> +int vfs_remove_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry)
> +{
> + struct inode *inode = dentry->d_inode;
> + int error;
> +
> + if (inode->i_op->set_fscaps)
> + error = inode->i_op->set_fscaps(idmap, dentry, NULL,
> + XATTR_REPLACE);
> + else
> + error = generic_remove_fscaps(idmap, dentry);
> +
> + return error;
> +}
> +
> +/**
> + * vfs_remove_fscaps - remove filesystem capabilities
> + * @idmap: idmap of the mount the inode was found from
> + * @dentry: the dentry from which to remove filesystem capabilities
> + *
> + * This function removes any filesystem capabilities from the specified
> + * dentry.
> + *
> + * Return: 0 on success, a negative errno on error.
> + */
> +int vfs_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry)
> +{
> + struct inode *inode = dentry->d_inode;
> + struct inode *delegated_inode = NULL;
> + int error;
> +
> +retry_deleg:
> + inode_lock(inode);
> +
> + error = xattr_permission(idmap, inode, XATTR_NAME_CAPS, MAY_WRITE);
> + if (error)
> + goto out_inode_unlock;

Should also use may_write_xattr() instead of xattr_permission() if
possible.

> +
> + error = security_inode_remove_fscaps(idmap, dentry);
> + if (error)
> + goto out_inode_unlock;
> +
> + error = try_break_deleg(inode, &delegated_inode);
> + if (error)
> + goto out_inode_unlock;
> +
> + error = vfs_remove_fscaps_nosec(idmap, dentry);
> + if (!error) {
> + fsnotify_xattr(dentry);
> + evm_inode_post_remove_fscaps(dentry);
> + }
> +
> +out_inode_unlock:
> + inode_unlock(inode);
> +
> + if (delegated_inode) {
> + error = break_deleg_wait(&delegated_inode);
> + if (!error)
> + goto retry_deleg;
> + }
> +
> + return error;
> +}
> +EXPORT_SYMBOL(vfs_remove_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 4f5d7ed44644..c07427d2fc71 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2122,6 +2122,8 @@ extern int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> struct vfs_caps *caps);
> extern int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> const struct vfs_caps *caps, int setxattr_flags);
> +extern int vfs_remove_fscaps_nosec(struct mnt_idmap *idmap, struct dentry *dentry);
> +extern int vfs_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry);

Please drop the extern.