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authorEric W. Biederman <ebiederm@xmission.com>2013-04-14 13:47:02 -0700
committerAndy Lutomirski <luto@amacapital.net>2013-04-14 18:11:14 -0700
commit6708075f104c3c9b04b23336bb0366ca30c3931b (patch)
tree4e99cf865cea3d809bfadda9eec45dcf29454bee /kernel
parent6c4c4d4bdaff7ec0b7b26da67d741f639727c934 (diff)
userns: Don't let unprivileged users trick privileged users into setting the id_map
When we require privilege for setting /proc/<pid>/uid_map or /proc/<pid>/gid_map no longer allow an unprivileged user to open the file and pass it to a privileged program to write to the file. Instead when privilege is required require both the opener and the writer to have the necessary capabilities. I have tested this code and verified that setting /proc/<pid>/uid_map fails when an unprivileged user opens the file and a privielged user attempts to set the mapping, that unprivileged users can still map their own id, and that a privileged users can still setup an arbitrary mapping. Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/user_namespace.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index a54f26f82eb2..e2d4ace4481b 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -25,7 +25,8 @@
static struct kmem_cache *user_ns_cachep __read_mostly;
-static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
+static bool new_idmap_permitted(const struct file *file,
+ struct user_namespace *ns, int cap_setid,
struct uid_gid_map *map);
static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
@@ -700,7 +701,7 @@ static ssize_t map_write(struct file *file, const char __user *buf,
ret = -EPERM;
/* Validate the user is allowed to use user id's mapped to. */
- if (!new_idmap_permitted(ns, cap_setid, &new_map))
+ if (!new_idmap_permitted(file, ns, cap_setid, &new_map))
goto out;
/* Map the lower ids from the parent user namespace to the
@@ -787,7 +788,8 @@ ssize_t proc_projid_map_write(struct file *file, const char __user *buf, size_t
&ns->projid_map, &ns->parent->projid_map);
}
-static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
+static bool new_idmap_permitted(const struct file *file,
+ struct user_namespace *ns, int cap_setid,
struct uid_gid_map *new_map)
{
/* Allow mapping to your own filesystem ids */
@@ -811,8 +813,10 @@ static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
/* Allow the specified ids if we have the appropriate capability
* (CAP_SETUID or CAP_SETGID) over the parent user namespace.
+ * And the opener of the id file also had the approprpiate capability.
*/
- if (ns_capable(ns->parent, cap_setid))
+ if (ns_capable(ns->parent, cap_setid) &&
+ file_ns_capable(file, ns->parent, cap_setid))
return true;
return false;