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>

1 files changed, 6 insertions, 3 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index dedf35f36971..4c3bd82cec49 100644
--- 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++) {