mm_for_maps: simplify, use ptrace_may_access()
It would be nice to kill __ptrace_may_access(). It requires task_lock(),
but this lock is only needed to read mm->flags in the middle.
Convert mm_for_maps() to use ptrace_may_access(), this also simplifies
the code a little bit.
Also, we do not need to take ->mmap_sem in advance. In fact I think
mm_for_maps() should not play with ->mmap_sem at all, the caller should
take this lock.
With or without this patch, without ->cred_guard_mutex held we can race
with exec() and get the new ->mm but check old creds.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3ce5ae9e..917f338 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -237,20 +237,19 @@
struct mm_struct *mm = get_task_mm(task);
if (!mm)
return NULL;
+ if (mm != current->mm) {
+ /*
+ * task->mm can be changed before security check,
+ * in that case we must notice the change after.
+ */
+ if (!ptrace_may_access(task, PTRACE_MODE_READ) ||
+ mm != task->mm) {
+ mmput(mm);
+ return NULL;
+ }
+ }
down_read(&mm->mmap_sem);
- task_lock(task);
- if (task->mm != mm)
- goto out;
- if (task->mm != current->mm &&
- __ptrace_may_access(task, PTRACE_MODE_READ) < 0)
- goto out;
- task_unlock(task);
return mm;
-out:
- task_unlock(task);
- up_read(&mm->mmap_sem);
- mmput(mm);
- return NULL;
}
static int proc_pid_cmdline(struct task_struct *task, char * buffer)