Commit 133bf750 authored Dec 08, 2023 by Max Kellermann Committed by Greg Kroah-Hartman Feb 23, 2024

fs/kernfs/dir: obey S_ISGID



[ Upstream commit 5133bee62f0ea5d4c316d503cc0040cac5637601 ]

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.

--
v1 -> v2: minor coding style fix (comment)

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20231208093310.297233-2-max.kellermann@ionos.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 17c252f1

fs/kernfs/dir.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -702,6 +702,18 @@ 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) {