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    Subject[PATCH 4.19 062/139] userfaultfd: shmem/hugetlbfs: only allow to register VM_MAYWRITE vmas
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

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

    From: Andrea Arcangeli <aarcange@redhat.com>

    commit 29ec90660d68bbdd69507c1c8b4e33aa299278b1 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/userfaultfd.c | 15 +++++++++++++++
    mm/userfaultfd.c | 15 ++++++---------
    2 files changed, 21 insertions(+), 9 deletions(-)

    --- a/fs/userfaultfd.c
    +++ b/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
    +++ b/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;
    @@ -449,13 +450,9 @@ 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;

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