On Thu 08-03-18 16:27:26, Mike Kravetz wrote:

A vma with vm_pgoff large enough to overflow a loff_t type when converted to a byte offset can be passed via the remap_file_pages system call. The hugetlbfs mmap routine uses the byte offset to calculate reservations and file size.

A sequence such as: mmap(0x20a00000, 0x600000, 0, 0x66033, -1, 0); remap_file_pages(0x20a00000, 0x600000, 0, 0x20000000000000, 0); will result in the following when task exits/file closed, kernel BUG at mm/hugetlb.c:749! Call Trace: hugetlbfs_evict_inode+0x2f/0x40 evict+0xcb/0x190 __dentry_kill+0xcb/0x150 __fput+0x164/0x1e0 task_work_run+0x84/0xa0 exit_to_usermode_loop+0x7d/0x80 do_syscall_64+0x18b/0x190 entry_SYSCALL_64_after_hwframe+0x3d/0xa2

The overflowed pgoff value causes hugetlbfs to try to set up a mapping with a negative range (end < start) that leaves invalid state which causes the BUG.

The previous overflow fix to this code was incomplete and did not take the remap_file_pages system call into account.

Fixes: 045c7a3f53d9 ("hugetlbfs: fix offset overflow in hugetlbfs mmap") Cc: stable@vger.kernel.org Reported-by: Nic Losby blurbdust@gmail.com Signed-off-by: Mike Kravetz mike.kravetz@oracle.com

OK, looks good to me. Hairy but seems to be the easiest way around this. Acked-by: Michal Hocko mhocko@suse.com

---

Changes in v3

• Use a simpler mask computation as suggested by Andrew Morton

Changes in v2

• Use bitmask for overflow check as suggested by Yisheng Xie
• Add explicit (from > to) check when setting up reservations
• Cc stable

fs/hugetlbfs/inode.c | 16 +++++++++++++--- mm/hugetlb.c | 6 ++++++ 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 8fe1b0aa2896..e46117dc006a 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -108,6 +108,15 @@ static void huge_pagevec_release(struct pagevec *pvec) pagevec_reinit(pvec); } +/*

• • Mask used when checking the page offset value passed in via system
• • calls. This value will be converted to a loff_t which is signed.
• • Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the
• • value. The extra bit (- 1 in the shift value) is to take the sign
• • bit into account.
• */

+#define PGOFF_LOFFT_MAX (PAGE_MASK << (BITS_PER_LONG - (2 * PAGE_SHIFT) - 1))

static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma) { struct inode *inode = file_inode(file); @@ -127,12 +136,13 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma) vma->vm_ops = &hugetlb_vm_ops; /*

• * Offset passed to mmap (before page shift) could have been
  

• * negative when represented as a (l)off_t.
  

• * page based offset in vm_pgoff could be sufficiently large to
  

• * overflow a (l)off_t when converted to byte offset.
  

  */

• if (((loff_t)vma->vm_pgoff << PAGE_SHIFT) < 0)

• if (vma->vm_pgoff & PGOFF_LOFFT_MAX) return -EINVAL;

• /* must be huge page aligned */ if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT)) return -EINVAL;

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7c204e3d132b..8eeade0a0b7a 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4374,6 +4374,12 @@ int hugetlb_reserve_pages(struct inode *inode, struct resv_map *resv_map; long gbl_reserve;

• /* This should never happen */
• if (from > to) {

• VM_WARN(1, "%s called with a negative range\n", __func__);
  

• return -EINVAL;
  

• }
• /*
  • Only apply hugepage reservation if asked. At fault time, an
  • attempt will be made for VM_NORESERVE to allocate a page

-- 2.13.6