From: Andrea Arcangeli <aarcange@redhat.com>
Date: Fri, 10 Mar 2017 00:16:28 +0000 (-0800)
Subject: userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE
X-Git-Tag: v4.4.107~96
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=ee9be99630398c907261042ed092612bcbfaa69d;p=thirdparty%2Fkernel%2Fstable.git

userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE


[ Upstream commit 6bbc4a4144b1a69743022ac68dfaf6e7d993abb9 ]

__do_fault assumes vmf->page has been initialized and is valid if
VM_FAULT_NOPAGE is not returned by vma->vm_ops->fault(vma, vmf).

handle_userfault() in turn should return VM_FAULT_NOPAGE if it doesn't
return VM_FAULT_SIGBUS or VM_FAULT_RETRY (the other two possibilities).

This VM_FAULT_NOPAGE case is only invoked when signal are pending and it
didn't matter for anonymous memory before.  It only started to matter
since shmem was introduced.  hugetlbfs also takes a different path and
doesn't exercise __do_fault.

Link: http://lkml.kernel.org/r/20170228154201.GH5816@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 66cdb44616d5a..59d58bdad7d3a 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -386,7 +386,7 @@ int handle_userfault(struct vm_area_struct *vma, unsigned long address,
 			 * in such case.
 			 */
 			down_read(&mm->mmap_sem);
-			ret = 0;
+			ret = VM_FAULT_NOPAGE;
 		}
 	}