CRED: Use RCU to access another task's creds and to release a task's own creds
Use RCU to access another task's creds and to release a task's own creds.
This means that it will be possible for the credentials of a task to be
replaced without another task (a) requiring a full lock to read them, and (b)
seeing deallocated memory.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b23492e..7555219 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1110,7 +1110,7 @@
const unsigned long __user *old_nodes,
const unsigned long __user *new_nodes)
{
- struct cred *cred, *tcred;
+ const struct cred *cred = current_cred(), *tcred;
struct mm_struct *mm;
struct task_struct *task;
nodemask_t old;
@@ -1145,14 +1145,16 @@
* capabilities, superuser privileges or the same
* userid as the target process.
*/
- cred = current->cred;
- tcred = task->cred;
+ rcu_read_lock();
+ tcred = __task_cred(task);
if (cred->euid != tcred->suid && cred->euid != tcred->uid &&
cred->uid != tcred->suid && cred->uid != tcred->uid &&
!capable(CAP_SYS_NICE)) {
+ rcu_read_unlock();
err = -EPERM;
goto out;
}
+ rcu_read_unlock();
task_nodes = cpuset_mems_allowed(task);
/* Is the user allowed to access the target nodes? */
diff --git a/mm/migrate.c b/mm/migrate.c
index 794443d..1422842 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1045,7 +1045,7 @@
const int __user *nodes,
int __user *status, int flags)
{
- struct cred *cred, *tcred;
+ const struct cred *cred = current_cred(), *tcred;
struct task_struct *task;
struct mm_struct *mm;
int err;
@@ -1076,14 +1076,16 @@
* capabilities, superuser privileges or the same
* userid as the target process.
*/
- cred = current->cred;
- tcred = task->cred;
+ rcu_read_lock();
+ tcred = __task_cred(task);
if (cred->euid != tcred->suid && cred->euid != tcred->uid &&
cred->uid != tcred->suid && cred->uid != tcred->uid &&
!capable(CAP_SYS_NICE)) {
+ rcu_read_unlock();
err = -EPERM;
goto out;
}
+ rcu_read_unlock();
err = security_task_movememory(task);
if (err)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 3af787b..0e0b282 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -298,9 +298,9 @@
task_lock(p);
printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
- p->pid, p->cred->uid, p->tgid, p->mm->total_vm,
- get_mm_rss(p->mm), (int)task_cpu(p), p->oomkilladj,
- p->comm);
+ p->pid, __task_cred(p)->uid, p->tgid,
+ p->mm->total_vm, get_mm_rss(p->mm), (int)task_cpu(p),
+ p->oomkilladj, p->comm);
task_unlock(p);
} while_each_thread(g, p);
}