Re: [PATCH v2 1/3] vfs: Add inode_sgid_strip() api

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Apr 14, 2022 at 03:57:17PM +0800, Yang Xu wrote:
> inode_sgid_strip() function is used to strip S_ISGID mode
> when creat/open/mknod file.
> 
> Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
> Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
> ---
>  fs/inode.c         | 18 ++++++++++++++++++
>  include/linux/fs.h |  3 ++-
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 9d9b422504d1..d63264998855 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2405,3 +2405,21 @@ struct timespec64 current_time(struct inode *inode)
>  	return timestamp_truncate(now, inode);
>  }
>  EXPORT_SYMBOL(current_time);
> +
> +void inode_sgid_strip(struct user_namespace *mnt_userns, struct inode *dir,
> +		      umode_t *mode)
> +{
> +	if (!dir || !(dir->i_mode & S_ISGID))
> +		return;
> +	if ((*mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
> +		return;
> +	if (S_ISDIR(*mode))
> +		return;
> +	if (in_group_p(i_gid_into_mnt(mnt_userns, dir)))
> +		return;
> +	if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
> +		return;
> +
> +	*mode &= ~S_ISGID;
> +}

Thanks for cleaning up the multiple if statements from last time.

I still would like to see patch 1 replace the code in inode_init_owner
so that we can compare before and after in the same patch.  Patch 2 can
then be solely about moving the callsite around the VFS.

--D

> +EXPORT_SYMBOL(inode_sgid_strip);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bbde95387a23..94d94219fe7c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1897,7 +1897,8 @@ extern long compat_ptr_ioctl(struct file *file, unsigned int cmd,
>  void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
>  		      const struct inode *dir, umode_t mode);
>  extern bool may_open_dev(const struct path *path);
> -
> +void inode_sgid_strip(struct user_namespace *mnt_userns, struct inode *dir,
> +		      umode_t *mode);
>  /*
>   * This is the "filldir" function type, used by readdir() to let
>   * the kernel specify what kind of dirent layout it wants to have.
> -- 
> 2.27.0
>