sysctl: allow to change limits for posix messages queues

All parameters of posix messages queues (queues_max/msg_max/msgsize_max)
end up being limited by RLIMIT_MSGQUEUE.  The code in mqueue_get_inode is
where that limiting happens.

The RLIMIT_MSGQUEUE is bound to the user namespace and is counted
hierarchically.

We can allow root in the user namespace to modify the posix messages
queues parameters.

Link: https://lkml.kernel.org/r/6ad67f23d1459a4f4339f74aa73bac0ecf3995e1.1705333426.git.legion@kernel.org
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Link: https://lkml.kernel.org/r/7eb21211c8622e91d226e63416b1b93c079f60ee.1663756794.git.legion@kernel.org
Cc: Christian Brauner <brauner@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Joel Granados <joel.granados@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
index ebb5ed81c151a8471f63df3fe61f94de51d30b79..21fba3a6edaf7a0c2e96c31ff34b761cff6b79e0 100644 (file)
--- a/ipc/mq_sysctl.c
+++ b/ipc/mq_sysctl.c
@@ -12,6 +12,7 @@
 #include <linux/stat.h>
 #include <linux/capability.h>
 #include <linux/slab.h>
+#include <linux/cred.h>
 
 static int msg_max_limit_min = MIN_MSGMAX;
 static int msg_max_limit_max = HARD_MSGMAX;
@@ -76,8 +77,43 @@ static int set_is_seen(struct ctl_table_set *set)
        return &current->nsproxy->ipc_ns->mq_set == set;
 }
 
+static void mq_set_ownership(struct ctl_table_header *head,
+                            struct ctl_table *table,
+                            kuid_t *uid, kgid_t *gid)
+{
+       struct ipc_namespace *ns =
+               container_of(head->set, struct ipc_namespace, mq_set);
+
+       kuid_t ns_root_uid = make_kuid(ns->user_ns, 0);
+       kgid_t ns_root_gid = make_kgid(ns->user_ns, 0);
+
+       *uid = uid_valid(ns_root_uid) ? ns_root_uid : GLOBAL_ROOT_UID;
+       *gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
+}
+
+static int mq_permissions(struct ctl_table_header *head, struct ctl_table *table)
+{
+       int mode = table->mode;
+       kuid_t ns_root_uid;
+       kgid_t ns_root_gid;
+
+       mq_set_ownership(head, table, &ns_root_uid, &ns_root_gid);
+
+       if (uid_eq(current_euid(), ns_root_uid))
+               mode >>= 6;
+
+       else if (in_egroup_p(ns_root_gid))
+               mode >>= 3;
+
+       mode &= 7;
+
+       return (mode << 6) | (mode << 3) | mode;
+}
+
 static struct ctl_table_root set_root = {
        .lookup = set_lookup,
+       .permissions = mq_permissions,
+       .set_ownership = mq_set_ownership,
 };
 
 bool setup_mq_sysctls(struct ipc_namespace *ns)