userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas
After the VMA to register the uffd onto is found, check that it has
VM_MAYWRITE set before allowing registration. This way we inherit all
common code checks before allowing to fill file holes in shmem and
hugetlbfs with UFFDIO_COPY.
The userfaultfd memory model is not applicable for readonly files unless
it's a MAP_PRIVATE.
Link: http://lkml.kernel.org/r/20181126173452.26955-4-aarcange@redhat.com
Fixes: ff62a3421044 ("hugetlb: implement memfd sealing")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Hugh Dickins <hughd@google.com>
Reported-by: Jann Horn <jannh@google.com>
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Cc: <stable@vger.kernel.org>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 356d2b85..cd58939 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1361,6 +1361,19 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
ret = -EINVAL;
if (!vma_can_userfault(cur))
goto out_unlock;
+
+ /*
+ * UFFDIO_COPY will fill file holes even without
+ * PROT_WRITE. This check enforces that if this is a
+ * MAP_SHARED, the process has write permission to the backing
+ * file. If VM_MAYWRITE is set it also enforces that on a
+ * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
+ * F_WRITE_SEAL can be taken until the vma is destroyed.
+ */
+ ret = -EPERM;
+ if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
+ goto out_unlock;
+
/*
* If this vma contains ending address, and huge pages
* check alignment.
@@ -1406,6 +1419,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
BUG_ON(!vma_can_userfault(vma));
BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
vma->vm_userfaultfd_ctx.ctx != ctx);
+ WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
/*
* Nothing to do: this vma is already registered into this
@@ -1552,6 +1566,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
cond_resched();
BUG_ON(!vma_can_userfault(vma));
+ WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
/*
* Nothing to do: this vma is already registered into this