From: Andrea Arcangeli aarcange@redhat.com Subject: userfaultfd: shmem: add i_size checks

With MAP_SHARED: recheck the i_size after taking the PT lock, to serialize against truncate with the PT lock. Delete the page from the pagecache if the i_size_read check fails.

With MAP_PRIVATE: check the i_size after the PT lock before mapping anonymous memory or zeropages into the MAP_PRIVATE shmem mapping.

A mostly irrelevant cleanup: like we do the delete_from_page_cache() pagecache removal after dropping the PT lock, the PT lock is a spinlock so drop it before the sleepable page lock.

Link: http://lkml.kernel.org/r/20181126173452.26955-5-aarcange@redhat.com Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support") 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 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 ---

mm/shmem.c | 18 ++++++++++++++++-- mm/userfaultfd.c | 26 ++++++++++++++++++++++++-- 2 files changed, 40 insertions(+), 4 deletions(-)

--- a/mm/shmem.c~userfaultfd-shmem-add-i_size-checks +++ a/mm/shmem.c @@ -2216,6 +2216,7 @@ static int shmem_mfill_atomic_pte(struct struct page *page; pte_t _dst_pte, *dst_pte; int ret; + pgoff_t offset, max_off;

ret = -ENOMEM; if (!shmem_inode_acct_block(inode, 1)) @@ -2253,6 +2254,12 @@ static int shmem_mfill_atomic_pte(struct __SetPageSwapBacked(page); __SetPageUptodate(page);

+ ret = -EFAULT; + offset = linear_page_index(dst_vma, dst_addr); + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + if (unlikely(offset >= max_off)) + goto out_release; + ret = mem_cgroup_try_charge_delay(page, dst_mm, gfp, &memcg, false); if (ret) goto out_release; @@ -2268,8 +2275,14 @@ static int shmem_mfill_atomic_pte(struct if (dst_vma->vm_flags & VM_WRITE) _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

- ret = -EEXIST; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); + + ret = -EFAULT; + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + if (unlikely(offset >= max_off)) + goto out_release_uncharge_unlock; + + ret = -EEXIST; if (!pte_none(*dst_pte)) goto out_release_uncharge_unlock;

@@ -2287,13 +2300,14 @@ static int shmem_mfill_atomic_pte(struct

/* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); - unlock_page(page); pte_unmap_unlock(dst_pte, ptl); + unlock_page(page); ret = 0; out: return ret; out_release_uncharge_unlock: pte_unmap_unlock(dst_pte, ptl); + delete_from_page_cache(page); out_release_uncharge: mem_cgroup_cancel_charge(page, memcg, false); out_release: --- a/mm/userfaultfd.c~userfaultfd-shmem-add-i_size-checks +++ a/mm/userfaultfd.c @@ -33,6 +33,8 @@ static int mcopy_atomic_pte(struct mm_st void *page_kaddr; int ret; struct page *page; + pgoff_t offset, max_off; + struct inode *inode;

if (!*pagep) { ret = -ENOMEM; @@ -73,8 +75,17 @@ static int mcopy_atomic_pte(struct mm_st if (dst_vma->vm_flags & VM_WRITE) _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

- ret = -EEXIST; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); + if (dst_vma->vm_file) { + /* the shmem MAP_PRIVATE case requires checking the i_size */ + inode = dst_vma->vm_file->f_inode; + offset = linear_page_index(dst_vma, dst_addr); + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + ret = -EFAULT; + if (unlikely(offset >= max_off)) + goto out_release_uncharge_unlock; + } + ret = -EEXIST; if (!pte_none(*dst_pte)) goto out_release_uncharge_unlock;

@@ -108,11 +119,22 @@ static int mfill_zeropage_pte(struct mm_ pte_t _dst_pte, *dst_pte; spinlock_t *ptl; int ret; + pgoff_t offset, max_off; + struct inode *inode;

_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr), dst_vma->vm_page_prot)); - ret = -EEXIST; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); + if (dst_vma->vm_file) { + /* the shmem MAP_PRIVATE case requires checking the i_size */ + inode = dst_vma->vm_file->f_inode; + offset = linear_page_index(dst_vma, dst_addr); + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + ret = -EFAULT; + if (unlikely(offset >= max_off)) + goto out_unlock; + } + ret = -EEXIST; if (!pte_none(*dst_pte)) goto out_unlock; set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); _