4.14-stable review patch. If anyone has any objections, please let me know.
------------------ From: Andrea Arcangeli <aarca...@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-aarca...@redhat.com Fixes: ff62a3421044 ("hugetlb: implement memfd sealing") Signed-off-by: Andrea Arcangeli <aarca...@redhat.com> Reviewed-by: Mike Rapoport <r...@linux.ibm.com> Reviewed-by: Hugh Dickins <hu...@google.com> Reported-by: Jann Horn <ja...@google.com> Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support") Cc: <sta...@vger.kernel.org> Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com> Cc: Mike Kravetz <mike.krav...@oracle.com> Cc: Peter Xu <pet...@redhat.com> Cc: sta...@vger.kernel.org Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gre...@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 @@ -1362,6 +1362,19 @@ 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. @@ -1407,6 +1420,7 @@ 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 @@ -1553,6 +1567,7 @@ 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 @@ -228,8 +228,9 @@ 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; @@ -472,13 +473,9 @@ 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;
