linux-kernel - [PATCH] userfaultfd: fix remap event with MREMAP

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Date:   Wed,  6 May 2020 10:21:58 -0700
From:   Brian Geffon <bgeffon@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Brian Geffon <bgeffon@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: [PATCH] userfaultfd: fix remap event with MREMAP_DONTUNMAP.

A user is not required to set a new address when using
MREMAP_DONTUNMAP as it can be used without MREMAP_FIXED.
When doing so the remap event will use new_addr which may not
have been set and we didn't propagate it back other then
in the return value of remap_to.

Because ret is always the new address it's probably more
correct to use it rather than new_addr on the remap_event_complete
call, and it resolves this bug.

Signed-off-by: Brian Geffon <bgeffon@...gle.com>
---
 mm/mremap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index c881abeba0bf..6aa6ea605068 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -794,7 +794,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 	if (locked && new_len > old_len)
 		mm_populate(new_addr + old_len, new_len - old_len);
 	userfaultfd_unmap_complete(mm, &uf_unmap_early);
-	mremap_userfaultfd_complete(&uf, addr, new_addr, old_len);
+	mremap_userfaultfd_complete(&uf, addr, ret, old_len);
 	userfaultfd_unmap_complete(mm, &uf_unmap);
 	return ret;
 }
-- 
2.26.2.526.g744177e7f7-goog