userfaultfd: hugetlbfs: prevent UFFDIO_COPY to fill beyond the end of i_size
This oops:
kernel BUG at fs/hugetlbfs/inode.c:484!
RIP: remove_inode_hugepages+0x3d0/0x410
Call Trace:
hugetlbfs_setattr+0xd9/0x130
notify_change+0x292/0x410
do_truncate+0x65/0xa0
do_sys_ftruncate.constprop.3+0x11a/0x180
SyS_ftruncate+0xe/0x10
tracesys+0xd9/0xde
was caused by the lack of i_size check in hugetlb_mcopy_atomic_pte.
mmap() can still succeed beyond the end of the i_size after vmtruncate
zapped vmas in those ranges, but the faults must not succeed, and that
includes UFFDIO_COPY.
We could differentiate the retval to userland to represent a SIGBUS like
a page fault would do (vs SIGSEGV), but it doesn't seem very useful and
we'd need to pick a random retval as there's no meaningful syscall
retval that would differentiate from SIGSEGV and SIGBUS, there's just
-EFAULT.
Link: http://lkml.kernel.org/r/20171016223914.2421-2-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@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/mm/hugetlb.c b/mm/hugetlb.c
index 424b0ef..2d2ff5e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3984,6 +3984,9 @@
unsigned long src_addr,
struct page **pagep)
{
+ struct address_space *mapping;
+ pgoff_t idx;
+ unsigned long size;
int vm_shared = dst_vma->vm_flags & VM_SHARED;
struct hstate *h = hstate_vma(dst_vma);
pte_t _dst_pte;
@@ -4021,13 +4024,24 @@
__SetPageUptodate(page);
set_page_huge_active(page);
+ mapping = dst_vma->vm_file->f_mapping;
+ idx = vma_hugecache_offset(h, dst_vma, dst_addr);
+
/*
* If shared, add to page cache
*/
if (vm_shared) {
- struct address_space *mapping = dst_vma->vm_file->f_mapping;
- pgoff_t idx = vma_hugecache_offset(h, dst_vma, dst_addr);
+ size = i_size_read(mapping->host) >> huge_page_shift(h);
+ ret = -EFAULT;
+ if (idx >= size)
+ goto out_release_nounlock;
+ /*
+ * Serialization between remove_inode_hugepages() and
+ * huge_add_to_page_cache() below happens through the
+ * hugetlb_fault_mutex_table that here must be hold by
+ * the caller.
+ */
ret = huge_add_to_page_cache(page, mapping, idx);
if (ret)
goto out_release_nounlock;
@@ -4036,6 +4050,20 @@
ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
spin_lock(ptl);
+ /*
+ * Recheck the i_size after holding PT lock to make sure not
+ * to leave any page mapped (as page_mapped()) beyond the end
+ * of the i_size (remove_inode_hugepages() is strict about
+ * enforcing that). If we bail out here, we'll also leave a
+ * page in the radix tree in the vm_shared case beyond the end
+ * of the i_size, but remove_inode_hugepages() will take care
+ * of it as soon as we drop the hugetlb_fault_mutex_table.
+ */
+ size = i_size_read(mapping->host) >> huge_page_shift(h);
+ ret = -EFAULT;
+ if (idx >= size)
+ goto out_release_unlock;
+
ret = -EEXIST;
if (!huge_pte_none(huge_ptep_get(dst_pte)))
goto out_release_unlock;
