Re: [PATCH v2] nfs: use vfs setgid helper

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2023-03-14 at 12:51 +0100, Christian Brauner wrote:
> We've aligned setgid behavior over multiple kernel releases. The details
> can be found in the following two merge messages:
> cf619f891971 ("Merge tag 'fs.ovl.setgid.v6.2')
> 426b4ca2d6a5 ("Merge tag 'fs.setgid.v6.0')
> Consistent setgid stripping behavior is now encapsulated in the
> setattr_should_drop_sgid() helper which is used by all filesystems that
> strip setgid bits outside of vfs proper. Switch nfs to rely on this
> helper as well. Without this patch the setgid stripping tests in
> xfstests will fail.
> 
> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
> ---
> Changes in v2:
> - Christoph Hellwig <hch@lst.de>:
>   * Export setattr_should_sgid() so it actually can be used by filesystems
> - Link to v1: https://lore.kernel.org/r/20230313-fs-nfs-setgid-v1-1-5b1fa599f186@kernel.org
> ---
>  fs/attr.c          | 1 +
>  fs/internal.h      | 2 --
>  fs/nfs/inode.c     | 4 +---
>  include/linux/fs.h | 2 ++
>  4 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/attr.c b/fs/attr.c
> index aca9ff7aed33..d60dc1edb526 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -47,6 +47,7 @@ int setattr_should_drop_sgid(struct mnt_idmap *idmap,
>  		return ATTR_KILL_SGID;
>  	return 0;
>  }
> +EXPORT_SYMBOL(setattr_should_drop_sgid);
>  
>  /**
>   * setattr_should_drop_suidgid - determine whether the set{g,u}id bit needs to
> diff --git a/fs/internal.h b/fs/internal.h
> index dc4eb91a577a..ab36ed8fa41c 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -259,8 +259,6 @@ ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *po
>  /*
>   * fs/attr.c
>   */
> -int setattr_should_drop_sgid(struct mnt_idmap *idmap,
> -			     const struct inode *inode);
>  struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns);
>  struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap);
>  void mnt_idmap_put(struct mnt_idmap *idmap);
> diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
> index 222a28320e1c..97a76706fd54 100644
> --- a/fs/nfs/inode.c
> +++ b/fs/nfs/inode.c
> @@ -717,9 +717,7 @@ void nfs_setattr_update_inode(struct inode *inode, struct iattr *attr,
>  		if ((attr->ia_valid & ATTR_KILL_SUID) != 0 &&
>  		    inode->i_mode & S_ISUID)
>  			inode->i_mode &= ~S_ISUID;
> -		if ((attr->ia_valid & ATTR_KILL_SGID) != 0 &&
> -		    (inode->i_mode & (S_ISGID | S_IXGRP)) ==
> -		     (S_ISGID | S_IXGRP))
> +		if (setattr_should_drop_sgid(&nop_mnt_idmap, inode))
>  			inode->i_mode &= ~S_ISGID;
>  		if ((attr->ia_valid & ATTR_MODE) != 0) {
>  			int mode = attr->ia_mode & S_IALLUGO;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c85916e9f7db..af95b64fc810 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2675,6 +2675,8 @@ extern struct inode *new_inode(struct super_block *sb);
>  extern void free_inode_nonrcu(struct inode *inode);
>  extern int setattr_should_drop_suidgid(struct mnt_idmap *, struct inode *);
>  extern int file_remove_privs(struct file *);
> +int setattr_should_drop_sgid(struct mnt_idmap *idmap,
> +			     const struct inode *inode);
>  
>  /*
>   * This must be used for allocating filesystems specific inodes to set
> 
> ---
> base-commit: eeac8ede17557680855031c6f305ece2378af326
> change-id: 20230313-fs-nfs-setgid-659410a10b25
> 

Reviewed-by: Jeff Layton <jlayton@kernel.org>