On Thu, Apr 21, 2022 at 03:54:15PM +0800, Yang Xu wrote:
> This has no functional change. Just create and export inode_sgid_strip
> api for the subsequent patch. This function is used to strip inode's
> S_ISGID mode when init a new inode.
>
> Signed-off-by: Yang Xu <xuyang2018.jy@xxxxxxxxxxx>
> ---
Could you please add the kernel doc I sketched below to the new helper?
Looks good to me,
Reviewed-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
> v4-v5:
> use umode_t return value instead of mode pointer
> fs/inode.c | 23 +++++++++++++++++++----
> include/linux/fs.h | 2 ++
> 2 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 9d9b422504d1..57130e4ef8b4 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2246,10 +2246,8 @@ void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
> /* Directories are special, and always inherit S_ISGID */
> if (S_ISDIR(mode))
> mode |= S_ISGID;
> - else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
> - !in_group_p(i_gid_into_mnt(mnt_userns, dir)) &&
> - !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
> - mode &= ~S_ISGID;
> + else
> + mode = inode_sgid_strip(mnt_userns, dir, mode);
> } else
> inode_fsgid_set(inode, mnt_userns);
> inode->i_mode = mode;
> @@ -2405,3 +2403,20 @@ struct timespec64 current_time(struct inode *inode)
> return timestamp_truncate(now, inode);
> }
> EXPORT_SYMBOL(current_time);
> +
/**
* inode_sgid_strip - handle the sgid bit for non-directories
* @mnt_userns: idmapping of the mount
* @dir: parent directory
* @mode: mode of the file to be created in @dir
*
* If the @mode of the new file has both the S_ISGID and S_IXGRP bit
* raised and @dir has the S_ISGID bit raised ensure that the caller is
* either in the group of the parent directory or they have CAP_FSETID
* in their user namespace and are privileged over the parent directory.
* In all other cases, strip the S_ISGID bit from @mode.
*
* Return: the new mode to use for the file
*/
> +umode_t inode_sgid_strip(struct user_namespace *mnt_userns,
> + const struct inode *dir, umode_t mode)
> +{
> + if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
> + return mode;
> + if ((mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
> + return mode;
> + if (in_group_p(i_gid_into_mnt(mnt_userns, dir)))
> + return mode;
> + if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
> + return mode;
> +
> + mode &= ~S_ISGID;
> + return mode;
> +}
> +EXPORT_SYMBOL(inode_sgid_strip);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bbde95387a23..532de76c9b91 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1897,6 +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);
> +umode_t inode_sgid_strip(struct user_namespace *mnt_userns,
> + const struct inode *dir, umode_t mode);
>
> /*
> * This is the "filldir" function type, used by readdir() to let
> --
> 2.27.0
>
