coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping

[sfrench/cifs-2.6.git] / include / linux / sched / mm.h

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 0cd9f10423fb8e60645685ab5bdbad675d803a51..a3fda9f024c3c1988b6ff60954d7f7e74a9c1ecf 100644 (file)
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -49,6 +49,27 @@ static inline void mmdrop(struct mm_struct *mm)
                __mmdrop(mm);
 }
 
+/*
+ * This has to be called after a get_task_mm()/mmget_not_zero()
+ * followed by taking the mmap_sem for writing before modifying the
+ * vmas or anything the coredump pretends not to change from under it.
+ *
+ * NOTE: find_extend_vma() called from GUP context is the only place
+ * that can modify the "mm" (notably the vm_start/end) under mmap_sem
+ * for reading and outside the context of the process, so it is also
+ * the only case that holds the mmap_sem for reading that must call
+ * this function. Generally if the mmap_sem is hold for reading
+ * there's no need of this check after get_task_mm()/mmget_not_zero().
+ *
+ * This function can be obsoleted and the check can be removed, after
+ * the coredump code will hold the mmap_sem for writing before
+ * invoking the ->core_dump methods.
+ */
+static inline bool mmget_still_valid(struct mm_struct *mm)
+{
+       return likely(!mm->core_state);
+}
+
 /**
  * mmget() - Pin the address space associated with a &struct mm_struct.
  * @mm: The address space to pin.