c/r: prctl: drop VMA flags test on PR_SET_MM_ stack data assignment

In commit b76437579d13 ("procfs: mark thread stack correctly in
proc/<pid>/maps") the stack allocated via clone() is marked in
/proc/<pid>/maps as [stack:%d] thus it might be out of the former
mm->start_stack/end_stack values (and even has some custom VMA flags
set).

So to be able to restore mm->start_stack/end_stack drop vma flags test,
but still require the underlying VMA to exist.

As always note this feature is under CONFIG_CHECKPOINT_RESTORE and
requires CAP_SYS_RESOURCE to be granted.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sys.c b/kernel/sys.c
index 0ec1942ba7ea6a60c19186efe859392079dc52f2..f0ec44dcd415de7d46601ebfb01e9a21dad02e85 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1786,14 +1786,6 @@ SYSCALL_DEFINE1(umask, int, mask)
 }
 
 #ifdef CONFIG_CHECKPOINT_RESTORE
-static bool vma_flags_mismatch(struct vm_area_struct *vma,
-                              unsigned long required,
-                              unsigned long banned)
-{
-       return (vma->vm_flags & required) != required ||
-               (vma->vm_flags & banned);
-}
-
 static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
 {
        struct vm_area_struct *vma;
@@ -1931,12 +1923,6 @@ static int prctl_set_mm(int opt, unsigned long addr,
                        error = -EFAULT;
                        goto out;
                }
-#ifdef CONFIG_STACK_GROWSUP
-               if (vma_flags_mismatch(vma, VM_READ | VM_WRITE | VM_GROWSUP, 0))
-#else
-               if (vma_flags_mismatch(vma, VM_READ | VM_WRITE | VM_GROWSDOWN, 0))
-#endif
-                       goto out;
                if (opt == PR_SET_MM_START_STACK)
                        mm->start_stack = addr;
                else if (opt == PR_SET_MM_ARG_START)