Re: [PATCH v7 08/15] fs: add __remove_file_privs() with flags parameter

Jan Kara
2022-06-02T09:04:28Z

On Wed 01-06-22 14:01:34, Stefan Roesch wrote:
> This adds the function __remove_file_privs, which allows the caller to
> pass the kiocb flags parameter.
>
> No intended functional changes in this patch.
>
> Signed-off-by: Stefan Roesch <shr@fb.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/inode.c | 57 +++++++++++++++++++++++++++++++++++-------------------
> 1 file changed, 37 insertions(+), 20 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 9d9b422504d1..ac1cf5aa78c8 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2010,36 +2010,43 @@ static int __remove_privs(struct user_namespace *mnt_userns,
> return notify_change(mnt_userns, dentry, &newattrs, NULL);
> }
>
> -/*
> - * Remove special file priviledges (suid, capabilities) when file is written
> - * to or truncated.
> - */
> -int file_remove_privs(struct file *file)
> +static int __file_remove_privs(struct file *file, unsigned int flags)
> {
> struct dentry *dentry = file_dentry(file);
> struct inode *inode = file_inode(file);
> + int error;
> int kill;
> - int error = 0;
>
> - /*
> - * Fast path for nothing security related.
> - * As well for non-regular files, e.g. blkdev inodes.
> - * For example, blkdev_write_iter() might get here
> - * trying to remove privs which it is not allowed to.
> - */
> if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
> return 0;
>
> kill = dentry_needs_remove_privs(dentry);
> - if (kill < 0)
> + if (kill <= 0)
> return kill;
> - if (kill)
> - error = __remove_privs(file_mnt_user_ns(file), dentry, kill);
> +
> + if (flags & IOCB_NOWAIT)
> + return -EAGAIN;
> +
> + error = __remove_privs(file_mnt_user_ns(file), dentry, kill);
> if (!error)
> inode_has_no_xattr(inode);
>
> return error;
> }
> +
> +/**
> + * file_remove_privs - remove special file privileges (suid, capabilities)
> + * @file: file to remove privileges from
> + *
> + * When file is modified by a write or truncation ensure that special
> + * file privileges are removed.
> + *
> + * Return: 0 on success, negative errno on failure.
> + */
> +int file_remove_privs(struct file *file)
> +{
> + return __file_remove_privs(file, 0);
> +}
> EXPORT_SYMBOL(file_remove_privs);
>
> /**
> @@ -2090,18 +2097,28 @@ int file_update_time(struct file *file)
> }
> EXPORT_SYMBOL(file_update_time);
>
> -/* Caller must hold the file's inode lock */
> +/**
> + * file_modified - handle mandated vfs changes when modifying a file
> + * @file: file that was modified
> + *
> + * When file has been modified ensure that special
> + * file privileges are removed and time settings are updated.
> + *
> + * Context: Caller must hold the file's inode lock.
> + *
> + * Return: 0 on success, negative errno on failure.
> + */
> int file_modified(struct file *file)
> {
> - int err;
> + int ret;
>
> /*
> * Clear the security bits if the process is not being run by root.
> * This keeps people from modifying setuid and setgid binaries.
> */
> - err = file_remove_privs(file);
> - if (err)
> - return err;
> + ret = __file_remove_privs(file, 0);
> + if (ret)
> + return ret;
>
> if (unlikely(file->f_mode & FMODE_NOCMTIME))
> return 0;
> --
> 2.30.2
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR