[PATCH v2 3/3] net: make net namespace sysctls belong to container's owner

[Dmitry Torokhov]

If net namespace is attached to a user namespace let's make container's
root owner of sysctls affecting said network namespace instead of global
root.

This also allows us to clean up net_ctl_permissions() because we do not
need to fudge permissions anymore for the container's owner since it now
owns the objects in question.

Acked-by: "Eric W. Biederman" <ebied...@xmission.com>
Signed-off-by: Dmitry Torokhov <dmitry.torok...@gmail.com>
---
 fs/proc/proc_sysctl.c  |  5 +++++
 include/linux/sysctl.h |  4 ++++
 net/sysctl_net.c       | 29 ++++++++++++++++++++---------
 3 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 5e57c3e..28f9085 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -430,6 +430,7 @@ static int sysctl_perm(struct ctl_table_header *head, 
struct ctl_table *table, i
 static struct inode *proc_sys_make_inode(struct super_block *sb,
                struct ctl_table_header *head, struct ctl_table *table)
 {
+       struct ctl_table_root *root = head->root;
        struct inode *inode;
        struct proc_inode *ei;
 
@@ -457,6 +458,10 @@ static struct inode *proc_sys_make_inode(struct 
super_block *sb,
                if (is_empty_dir(head))
                        make_empty_dir_inode(inode);
        }
+
+       if (root->set_ownership)
+               root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);
+
 out:
        return inode;
 }
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index fa7bc29..55bec2f 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -25,6 +25,7 @@
 #include <linux/rcupdate.h>
 #include <linux/wait.h>
 #include <linux/rbtree.h>
+#include <linux/uidgid.h>
 #include <uapi/linux/sysctl.h>
 
 /* For the /proc/sys support */
@@ -156,6 +157,9 @@ struct ctl_table_root {
        struct ctl_table_set default_set;
        struct ctl_table_set *(*lookup)(struct ctl_table_root *root,
                                           struct nsproxy *namespaces);
+       void (*set_ownership)(struct ctl_table_header *head,
+                             struct ctl_table *table,
+                             kuid_t *uid, kgid_t *gid);
        int (*permissions)(struct ctl_table_header *head, struct ctl_table 
*table);
 };
 
diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index ed98c1f..5bc1a3d 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -42,26 +42,37 @@ static int net_ctl_permissions(struct ctl_table_header 
*head,
                               struct ctl_table *table)
 {
        struct net *net = container_of(head->set, struct net, sysctls);
-       kuid_t root_uid = make_kuid(net->user_ns, 0);
-       kgid_t root_gid = make_kgid(net->user_ns, 0);
 
        /* Allow network administrator to have same access as root. */
-       if (ns_capable(net->user_ns, CAP_NET_ADMIN) ||
-           uid_eq(root_uid, current_euid())) {
+       if (ns_capable(net->user_ns, CAP_NET_ADMIN)) {
                int mode = (table->mode >> 6) & 7;
                return (mode << 6) | (mode << 3) | mode;
        }
-       /* Allow netns root group to have the same access as the root group */
-       if (in_egroup_p(root_gid)) {
-               int mode = (table->mode >> 3) & 7;
-               return (mode << 3) | mode;
-       }
+
        return table->mode;
 }
 
+static void net_ctl_set_ownership(struct ctl_table_header *head,
+                                 struct ctl_table *table,
+                                 kuid_t *uid, kgid_t *gid)
+{
+       struct net *net = container_of(head->set, struct net, sysctls);
+       kuid_t ns_root_uid;
+       kgid_t ns_root_gid;
+
+       ns_root_uid = make_kuid(net->user_ns, 0);
+       if (uid_valid(ns_root_uid))
+               *uid = ns_root_uid;
+
+       ns_root_gid = make_kgid(net->user_ns, 0);
+       if (gid_valid(ns_root_gid))
+               *gid = ns_root_gid;
+}
+
 static struct ctl_table_root net_sysctl_root = {
        .lookup = net_ctl_header_lookup,
        .permissions = net_ctl_permissions,
+       .set_ownership = net_ctl_set_ownership,
 };
 
 static int __net_init sysctl_net_init(struct net *net)
-- 
2.8.0.rc3.226.g39d4020