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

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

On Fri, Apr 15, 2022 at 01:18:57AM +0000, xuyang2018.jy@fujitsu.com wrote:
> on 2022/4/14 23:57, Darrick J. Wong wrote:
> > 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.
> >
> Ok, then patch 1 can named as"fs/inode: move inode sgid strip operation 
> from inode_init_owner into inode_sgid_strip".  What do you think about it?

Sounds good to me.

--D

> 
> Best Regards
> Yang Xu
> > --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
> >>