keys: don't generate user and user session keyrings unless they're accessed

Don't generate the per-UID user and user session keyrings unless they're
explicitly accessed.  This solves a problem during a login process whereby
set*uid() is called before the SELinux PAM module, resulting in the per-UID
keyrings having the wrong security labels.

This also cures the problem of multiple per-UID keyrings sometimes appearing
due to PAM modules (including pam_keyinit) setuiding and causing user_structs
to come into and go out of existence whilst the session keyring pins the user
keyring.  This is achieved by first searching for extant per-UID keyrings
before inventing new ones.

The serial bound argument is also dropped from find_keyring_by_name() as it's
not currently made use of (setting it to 0 disables the feature).

Signed-off-by: David Howells <dhowells@redhat.com>
Cc: <kwc@citi.umich.edu>
Cc: <arunsr@cse.iitk.ac.in>
Cc: <dwalsh@redhat.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 11 deletions

diff --git a/kernel/user.c b/kernel/user.c
index debce602bfdd..aefbbfa3159f 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -53,10 +53,6 @@ struct user_struct root_user = {
         .files          = ATOMIC_INIT(0),
         .sigpending     = ATOMIC_INIT(0),
         .locked_shm     = 0,
-#ifdef CONFIG_KEYS
-        .uid_keyring    = &root_user_keyring,
-        .session_keyring = &root_session_keyring,
-#endif
 #ifdef CONFIG_USER_SCHED
         .tg             = &init_task_group,
 #endif
@@ -420,12 +416,12 @@ struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
                 new->mq_bytes = 0;
 #endif
                 new->locked_shm = 0;
-
-                if (alloc_uid_keyring(new, current) < 0)
-                        goto out_free_user;
+#ifdef CONFIG_KEYS
+                new->uid_keyring = new->session_keyring = NULL;
+#endif
 
                 if (sched_create_user(new) < 0)
-                        goto out_put_keys;
+                        goto out_free_user;
 
                 if (uids_user_create(new))
                         goto out_destoy_sched;
@@ -459,9 +455,6 @@ struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
 
 out_destoy_sched:
         sched_destroy_user(new);
-out_put_keys:
-        key_put(new->uid_keyring);
-        key_put(new->session_keyring);
 out_free_user:
         kmem_cache_free(uid_cachep, new);
 out_unlock: