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SubjectRe: [PATCH v3] hugetlbfs: check for pgoff value overflow
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

--
Michal Hocko
SUSE Labs

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