[PATCH 4.12 019/106] userfaultfd: non-cooperative: notify about unmap of destination during mremap

[Greg Kroah-Hartman]

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

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

From: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>

commit b22823719302e88d0e2a6bb06433bd97b175a8d8 upstream.

When mremap is called with MREMAP_FIXED it unmaps memory at the
destination address without notifying userfaultfd monitor.

If the destination were registered with userfaultfd, the monitor has no
way to distinguish between the old and new ranges and to properly relate
the page faults that would occur in the destination region.

Fixes: 897ab3e0c49e ("userfaultfd: non-cooperative: add event for memory unmaps")
Link: http://lkml.kernel.org/r/1500276876-3350-1-git-send-email-rppt@xxxxxxxxxxxxxxxxxx
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/mremap.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -429,6 +429,7 @@ static struct vm_area_struct *vma_to_res
 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 		unsigned long new_addr, unsigned long new_len, bool *locked,
 		struct vm_userfaultfd_ctx *uf,
+		struct list_head *uf_unmap_early,
 		struct list_head *uf_unmap)
 {
 	struct mm_struct *mm = current->mm;
@@ -447,7 +448,7 @@ static unsigned long mremap_to(unsigned
 	if (addr + old_len > new_addr && new_addr + new_len > addr)
 		goto out;
 
-	ret = do_munmap(mm, new_addr, new_len, NULL);
+	ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 	if (ret)
 		goto out;
 
@@ -515,6 +516,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, a
 	unsigned long charged = 0;
 	bool locked = false;
 	struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
+	LIST_HEAD(uf_unmap_early);
 	LIST_HEAD(uf_unmap);
 
 	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
@@ -542,7 +544,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, a
 
 	if (flags & MREMAP_FIXED) {
 		ret = mremap_to(addr, old_len, new_addr, new_len,
-				&locked, &uf, &uf_unmap);
+				&locked, &uf, &uf_unmap_early, &uf_unmap);
 		goto out;
 	}
 
@@ -622,6 +624,7 @@ out:
 	up_write(&current->mm->mmap_sem);
 	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);
 	userfaultfd_unmap_complete(mm, &uf_unmap);
 	return ret;