Commit 704b836c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by James Morris
Browse files

mm_for_maps: take ->cred_guard_mutex to fix the race with exec

The problem is minor, but without ->cred_guard_mutex held we can race
with exec() and get the new ->mm but check old creds.

Now we do not need to re-check task->mm after ptrace_may_access(), it
can't be changed to the new mm under us.

Strictly speaking, this also fixes another very minor problem. Unless
security check fails or the task exits mm_for_maps() should never
return NULL, the caller should get either old or new ->mm.
Signed-off-by: default avatarOleg Nesterov <>
Acked-by: default avatarSerge Hallyn <>
Signed-off-by: default avatarJames Morris <>
parent 00f89d21
...@@ -234,19 +234,19 @@ static int check_mem_permission(struct task_struct *task) ...@@ -234,19 +234,19 @@ static int check_mem_permission(struct task_struct *task)
struct mm_struct *mm_for_maps(struct task_struct *task) struct mm_struct *mm_for_maps(struct task_struct *task)
{ {
struct mm_struct *mm = get_task_mm(task); struct mm_struct *mm;
if (mm && mm != current->mm) { if (mutex_lock_killable(&task->cred_guard_mutex))
/* return NULL;
* task->mm can be changed before security check,
* in that case we must notice the change after. mm = get_task_mm(task);
*/ if (mm && mm != current->mm &&
if (!ptrace_may_access(task, PTRACE_MODE_READ) || !ptrace_may_access(task, PTRACE_MODE_READ)) {
mm != task->mm) {
mmput(mm); mmput(mm);
mm = NULL; mm = NULL;
} }
} mutex_unlock(&task->cred_guard_mutex);
return mm; return mm;
} }
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