tracing/stack-tracer: fix locking and refcounts

Impact: fix refcounting/object-access bug

Hold mmap_sem while looking up/accessing vma.
Hold the RCU lock while using the task we looked up.

Signed-off-by: Török Edwin <edwintorok@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dedf35f369719d32d2fb1be68137429c68a764a7..4c3bd82cec49c9debaf16c85a80cdaa3d83580b8 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1462,11 +1462,15 @@ static inline int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
        int ret = 1;
 
        if (mm) {
-               const struct vm_area_struct *vma = find_vma(mm, ip);
+               const struct vm_area_struct *vma;
+
+               down_read(&mm->mmap_sem);
+               vma = find_vma(mm, ip);
                if (vma) {
                        file = vma->vm_file;
                        vmstart = vma->vm_start;
                }
+               up_read(&mm->mmap_sem);
        }
        if (file) {
                ret = trace_seq_path(s, &file->f_path);
@@ -1494,10 +1498,9 @@ seq_print_userip_objs(const struct userstack_entry *entry, struct trace_seq *s,
                 */
                rcu_read_lock();
                task = find_task_by_vpid(entry->ent.tgid);
-               rcu_read_unlock();
-
                if (task)
                        mm = get_task_mm(task);
+               rcu_read_unlock();
        }
 
        for (i = 0; i < FTRACE_STACK_ENTRIES; i++) {