scm: Require CAP_SYS_ADMIN over the current pidns to spoof pids.

Don't allow spoofing pids over unix domain sockets in the corner
cases where a user has created a user namespace but has not yet
created a pid namespace.

Cc: stable@vger.kernel.org
Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/net/core/scm.c b/net/core/scm.c
index 905dcc6ad1e3b480c01f87df5157f4e37de112a1..2dc6cdaaae8abc5f31afa57a7ccf765cc978b6ac 100644 (file)
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -24,6 +24,7 @@
 #include <linux/interrupt.h>
 #include <linux/netdevice.h>
 #include <linux/security.h>
+#include <linux/pid_namespace.h>
 #include <linux/pid.h>
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
@@ -52,7 +53,8 @@ static __inline__ int scm_check_creds(struct ucred *creds)
        if (!uid_valid(uid) || !gid_valid(gid))
                return -EINVAL;
 
-       if ((creds->pid == task_tgid_vnr(current) || nsown_capable(CAP_SYS_ADMIN)) &&
+       if ((creds->pid == task_tgid_vnr(current) ||
+            ns_capable(current->nsproxy->pid_ns->user_ns, CAP_SYS_ADMIN)) &&
            ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
              uid_eq(uid, cred->suid)) || nsown_capable(CAP_SETUID)) &&
            ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||