From 133bf750d75e73926283cf621be7387c60e14818 Mon Sep 17 00:00:00 2001 From: Max Kellermann Date: Fri, 8 Dec 2023 10:33:10 +0100 Subject: [PATCH] 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 Acked-by: Tejun Heo Link: https://lore.kernel.org/r/20231208093310.297233-2-max.kellermann@ionos.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- fs/kernfs/dir.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index d2068566c0b8..d3a602ea795b 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -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) {