MIPS: VDSO: Prevent use of smp_processor_id()

[android-x86/kernel.git] / kernel / cred.c

diff --git a/kernel/cred.c b/kernel/cred.c
index 5f264fb..0966fab 100644 (file)
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -146,7 +146,10 @@ void __put_cred(struct cred *cred)
        BUG_ON(cred == current->cred);
        BUG_ON(cred == current->real_cred);
 
-       call_rcu(&cred->rcu, put_cred_rcu);
+       if (cred->non_rcu)
+               put_cred_rcu(&cred->rcu);
+       else
+               call_rcu(&cred->rcu, put_cred_rcu);
 }
 EXPORT_SYMBOL(__put_cred);
 
@@ -257,6 +260,7 @@ struct cred *prepare_creds(void)
        old = task->cred;
        memcpy(new, old, sizeof(struct cred));
 
+       new->non_rcu = 0;
        atomic_set(&new->usage, 1);
        set_cred_subscribers(new, 0);
        get_group_info(new->group_info);
@@ -447,6 +451,15 @@ int commit_creds(struct cred *new)
                if (task->mm)
                        set_dumpable(task->mm, suid_dumpable);
                task->pdeath_signal = 0;
+               /*
+                * If a task drops privileges and becomes nondumpable,
+                * the dumpability change must become visible before
+                * the credential change; otherwise, a __ptrace_may_access()
+                * racing with this change may be able to attach to a task it
+                * shouldn't be able to attach to (as if the task had dropped
+                * privileges without becoming nondumpable).
+                * Pairs with a read barrier in __ptrace_may_access().
+                */
                smp_wmb();
        }
 
@@ -527,7 +540,19 @@ const struct cred *override_creds(const struct cred *new)
 
        validate_creds(old);
        validate_creds(new);
-       get_cred(new);
+
+       /*
+        * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
+        *
+        * That means that we do not clear the 'non_rcu' flag, since
+        * we are only installing the cred into the thread-synchronous
+        * '->cred' pointer, not the '->real_cred' pointer that is
+        * visible to other threads under RCU.
+        *
+        * Also note that we did validate_creds() manually, not depending
+        * on the validation in 'get_cred()'.
+        */
+       get_new_cred((struct cred *)new);
        alter_cred_subscribers(new, 1);
        rcu_assign_pointer(current->cred, new);
        alter_cred_subscribers(old, -1);
@@ -610,6 +635,7 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
        validate_creds(old);
 
        *new = *old;
+       new->non_rcu = 0;
        atomic_set(&new->usage, 1);
        set_cred_subscribers(new, 0);
        get_uid(new->user);