On Fri, Dec 08, 2023 at 10:33:10AM +0100, Max Kellermann wrote:
> Handling of S_ISGID is usually done by inode_init_owner() in all other
> filesystems, but kernfs doesn't use that function. In kernfs, struct
> kernfs_node is the primary data structure, and struct inode is only
> created from it on demand. Therefore, inode_init_owner() can't be
> used and we need to imitate its behavior.
>
> S_ISGID support is useful for the cgroup filesystem; it allows
> subtrees managed by an unprivileged process to retain a certain owner
> gid, which then enables sharing access to the subtree with another
> unprivileged process.
>
> Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>
> --
> v1 -> v2: minor coding style fix (comment)
> ---
> fs/kernfs/dir.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index 8b2bd65d70e7..62d39ecf0a46 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -676,6 +676,18 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
> {
> struct kernfs_node *kn;
>
> + if (parent->mode & S_ISGID) {
> + /* this code block imitates inode_init_owner() for
> + * kernfs
> + */
> +
> + if (parent->iattr)
> + gid = parent->iattr->ia_gid;
> +
> + if (flags & KERNFS_DIR)
> + mode |= S_ISGID;
> + }
> +
> kn = __kernfs_new_node(kernfs_root(parent), parent,
> name, mode, uid, gid, flags);
> if (kn) {
No noticeable regressions with this patch applied.
Tested-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>
--
An old man doll... just what I always wanted! - Clara
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