linux-kernel - [PATCH 4.12 020/106] userfaultfd_zeropage: return -ENOSPC in case mm has gone

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Date:   Wed,  9 Aug 2017 09:52:04 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.12 020/106] userfaultfd_zeropage: return -ENOSPC in case mm has gone

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Rapoport <rppt@...ux.vnet.ibm.com>

commit 9d95aa4bada24be35bb94827a55e1d6e243d866e upstream.

In the non-cooperative userfaultfd case, the process exit may race with
outstanding mcopy_atomic called by the uffd monitor.  Returning -ENOSPC
instead of -EINVAL when mm is already gone will allow uffd monitor to
distinguish this case from other error conditions.

Unfortunately I overlooked userfaultfd_zeropage when updating
userfaultd_copy().

Link: http://lkml.kernel.org/r/1501136819-21857-1-git-send-email-rppt@linux.vnet.ibm.com
Fixes: 96333187ab162 ("userfaultfd_copy: return -ENOSPC in case mm has gone")
Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Cc: Pavel Emelyanov <xemul@...tuozzo.com>
Cc: Michal Hocko <mhocko@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/userfaultfd.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1645,6 +1645,8 @@ static int userfaultfd_zeropage(struct u
 		ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
 				     uffdio_zeropage.range.len);
 		mmput(ctx->mm);
+	} else {
+		return -ENOSPC;
 	}
 	if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
 		return -EFAULT;