linux-kernel - [PATCH] mm/userfaultfd: Reset ptes when close() for wr-protected ones

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Date: Mon, 22 Apr 2024 09:33:11 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: peterx@...hat.com,
	Nadav Amit <nadav.amit@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	syzbot+d8426b591c36b21c750e@...kaller.appspotmail.com
Subject: [PATCH] mm/userfaultfd: Reset ptes when close() for wr-protected ones

Userfaultfd unregister includes a step to remove wr-protect bits from all
the relevant pgtable entries, but that only covered an explicit
UFFDIO_UNREGISTER ioctl, not a close() on the userfaultfd itself.  Cover
that too.

Link: https://lore.kernel.org/all/000000000000ca4df20616a0fe16@google.com/
Analyzed-by: David Hildenbrand <david@...hat.com>
Reported-by: syzbot+d8426b591c36b21c750e@...kaller.appspotmail.com
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 fs/userfaultfd.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 3e6ddda6f159..d2c3879745e5 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -898,6 +898,10 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 			prev = vma;
 			continue;
 		}
+		/* Reset ptes for the whole vma range if wr-protected */
+		if (userfaultfd_wp(vma))
+			uffd_wp_range(vma, vma->vm_start,
+				      vma->vm_end - vma->vm_start, false);
 		new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
 		vma = vma_modify_flags_uffd(&vmi, prev, vma, vma->vm_start,
 					    vma->vm_end, new_flags,
-- 
2.44.0