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5e4a08476b
Andy Lutomirski <luto@amacapital.net> found a nasty little bug in
the permissions of setns. With unprivileged user namespaces it
became possible to create new namespaces without privilege.
However the setns calls were relaxed to only require CAP_SYS_ADMIN in
the user nameapce of the targed namespace.
Which made the following nasty sequence possible.
pid = clone(CLONE_NEWUSER | CLONE_NEWNS);
if (pid == 0) { /* child */
system("mount --bind /home/me/passwd /etc/passwd");
}
else if (pid != 0) { /* parent */
char path[PATH_MAX];
snprintf(path, sizeof(path), "/proc/%u/ns/mnt");
fd = open(path, O_RDONLY);
setns(fd, 0);
system("su -");
}
Prevent this possibility by requiring CAP_SYS_ADMIN
in the current user namespace when joing all but the user namespace.
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
141 lines
2.8 KiB
C
141 lines
2.8 KiB
C
/*
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* Copyright (C) 2004 IBM Corporation
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*
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* Author: Serge Hallyn <serue@us.ibm.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation, version 2 of the
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* License.
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*/
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#include <linux/export.h>
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#include <linux/uts.h>
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#include <linux/utsname.h>
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#include <linux/err.h>
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#include <linux/slab.h>
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#include <linux/user_namespace.h>
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#include <linux/proc_fs.h>
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static struct uts_namespace *create_uts_ns(void)
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{
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struct uts_namespace *uts_ns;
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uts_ns = kmalloc(sizeof(struct uts_namespace), GFP_KERNEL);
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if (uts_ns)
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kref_init(&uts_ns->kref);
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return uts_ns;
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}
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/*
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* Clone a new ns copying an original utsname, setting refcount to 1
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* @old_ns: namespace to clone
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* Return NULL on error (failure to kmalloc), new ns otherwise
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*/
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static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
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struct uts_namespace *old_ns)
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{
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struct uts_namespace *ns;
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int err;
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ns = create_uts_ns();
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if (!ns)
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return ERR_PTR(-ENOMEM);
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err = proc_alloc_inum(&ns->proc_inum);
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if (err) {
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kfree(ns);
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return ERR_PTR(err);
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}
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down_read(&uts_sem);
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memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
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ns->user_ns = get_user_ns(user_ns);
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up_read(&uts_sem);
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return ns;
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}
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/*
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* Copy task tsk's utsname namespace, or clone it if flags
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* specifies CLONE_NEWUTS. In latter case, changes to the
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* utsname of this process won't be seen by parent, and vice
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* versa.
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*/
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struct uts_namespace *copy_utsname(unsigned long flags,
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struct user_namespace *user_ns, struct uts_namespace *old_ns)
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{
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struct uts_namespace *new_ns;
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BUG_ON(!old_ns);
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get_uts_ns(old_ns);
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if (!(flags & CLONE_NEWUTS))
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return old_ns;
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new_ns = clone_uts_ns(user_ns, old_ns);
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put_uts_ns(old_ns);
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return new_ns;
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}
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void free_uts_ns(struct kref *kref)
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{
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struct uts_namespace *ns;
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ns = container_of(kref, struct uts_namespace, kref);
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put_user_ns(ns->user_ns);
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proc_free_inum(ns->proc_inum);
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kfree(ns);
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}
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static void *utsns_get(struct task_struct *task)
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{
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struct uts_namespace *ns = NULL;
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struct nsproxy *nsproxy;
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rcu_read_lock();
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nsproxy = task_nsproxy(task);
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if (nsproxy) {
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ns = nsproxy->uts_ns;
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get_uts_ns(ns);
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}
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rcu_read_unlock();
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return ns;
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}
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static void utsns_put(void *ns)
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{
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put_uts_ns(ns);
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}
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static int utsns_install(struct nsproxy *nsproxy, void *new)
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{
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struct uts_namespace *ns = new;
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if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
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!nsown_capable(CAP_SYS_ADMIN))
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return -EPERM;
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get_uts_ns(ns);
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put_uts_ns(nsproxy->uts_ns);
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nsproxy->uts_ns = ns;
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return 0;
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}
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static unsigned int utsns_inum(void *vp)
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{
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struct uts_namespace *ns = vp;
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return ns->proc_inum;
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}
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const struct proc_ns_operations utsns_operations = {
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.name = "uts",
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.type = CLONE_NEWUTS,
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.get = utsns_get,
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.put = utsns_put,
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.install = utsns_install,
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.inum = utsns_inum,
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};
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