[PATCH v2] fs/proc/proc_sysctl.c: always initialize i_uid/i_gid

Commit e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
added default values for i_uid/i_gid.
These however are only used when ctl_table_root->set_ownership is not
implemented.
But the callbacks themselves could fail to compute i_uid/i_gid and they
all need to have the same fallback logic for this case.

This is unnecessary code duplication and prone to errors.
For example net_ctl_set_ownership() missed the fallback.

Instead always initialize i_uid/i_gid inside the sysfs core so
set_ownership() can safely skip setting them.

Fixes: e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Changes in v2:
- Move the fallback logic to the sysctl core
- Link to v1: https://lore.kernel.org/r/20240315-sysctl-net-ownership-v1-1-2b465555a292@weissschuh.net (local)
---
 fs/proc/proc_sysctl.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 37cde0efee57..9e34ab9c21e4 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c

@@ -479,12 +479,10 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
 			make_empty_dir_inode(inode);
 	}
 
+	inode->i_uid = GLOBAL_ROOT_UID;
+	inode->i_gid = GLOBAL_ROOT_GID;
 	if (root->set_ownership)
 		root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);
-	else {
-		inode->i_uid = GLOBAL_ROOT_UID;
-		inode->i_gid = GLOBAL_ROOT_GID;
-	}
 
 	return inode;
 }

---
base-commit: ff9c18e435b042596c9d48badac7488e3fa76a55
change-id: 20240315-sysctl-net-ownership-bc4e17eaeea6

Best regards,
-- 
Thomas Weißschuh [off-list ref]