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fs/kernfs/dir: obey S_ISGID

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[ 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>
This commit is contained in:
Max Kellermann 2023-12-08 10:33:10 +01:00 • committed by Ksawlii
parent 8ca1a9ecc1
commit 53357db04a
1 changed files with 12 additions and 0 deletions
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12
fs/kernfs/dir.c
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@ -696,6 +696,18 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
{ {
struct kernfs_node *kn; 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, kn = __kernfs_new_node(kernfs_root(parent), parent,
name, mode, uid, gid, flags); name, mode, uid, gid, flags);
if (kn) { if (kn) {