The patch titled
Subject: userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas
has been added to the -mm tree. Its filename is
userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas.patch
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The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Fixes: ff62a3421044 ("hugetlb: implement memfd sealing")
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Reviewed-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/fs/userfaultfd.c~userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas
+++ a/fs/userfaultfd.c
@@ -1361,6 +1361,19 @@ static int userfaultfd_register(struct u
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 u
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
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
--- a/mm/userfaultfd.c~userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas
+++ a/mm/userfaultfd.c
@@ -205,8 +205,9 @@ retry:
if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
goto out_unlock;
/*
- * Only allow __mcopy_atomic_hugetlb on userfaultfd
- * registered ranges.
+ * Check the vma is registered in uffd, this is
+ * required to enforce the VM_MAYWRITE check done at
+ * uffd registration time.
*/
if (!dst_vma->vm_userfaultfd_ctx.ctx)
goto out_unlock;
@@ -459,13 +460,9 @@ retry:
if (!dst_vma)
goto out_unlock;
/*
- * Be strict and only allow __mcopy_atomic on userfaultfd
- * registered ranges to prevent userland errors going
- * unnoticed. As far as the VM consistency is concerned, it
- * would be perfectly safe to remove this check, but there's
- * no useful usage for __mcopy_atomic ouside of userfaultfd
- * registered ranges. This is after all why these are ioctls
- * belonging to the userfaultfd and not syscalls.
+ * Check the vma is registered in uffd, this is required to
+ * enforce the VM_MAYWRITE check done at uffd registration
+ * time.
*/
if (!dst_vma->vm_userfaultfd_ctx.ctx)
goto out_unlock;
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails.patch
userfaultfd-shmem-allocate-anonymous-memory-for-map_private-shmem.patch
userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas.patch
userfaultfd-shmem-add-i_size-checks.patch
userfaultfd-shmem-uffdio_copy-set-the-page-dirty-if-vm_write-is-not-set.patch
