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) {
--
2.39.2
