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Commit 63489f8e authored by Mike Kravetz's avatar Mike Kravetz Committed by Linus Torvalds
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hugetlbfs: check for pgoff value overflow 

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.

[mike.kravetz@oracle.com: v3]
  Link: http://lkml.kernel.org/r/20180309002726.7248-1-mike.kravetz@oracle.com
[akpm@linux-foundation.org: include mmdebug.h]
[akpm@linux-foundation.org: fix -ve left shift count on sh]
Link: http://lkml.kernel.org/r/20180308210502.15952-1-mike.kravetz@oracle.com


Fixes: 045c7a3f ("hugetlbfs: fix offset overflow in hugetlbfs mmap")
Signed-off-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Reported-by: default avatarNic Losby <blurbdust@gmail.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2e517d68

fs/hugetlbfs/inode.c

+14 −3
Original line number Diff line number Diff line
@@ -108,6 +108,16 @@ 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 \

	(((1UL << (PAGE_SHIFT + 1)) - 1) <<  (BITS_PER_LONG - (PAGE_SHIFT + 1)))



static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)

{

	struct inode *inode = file_inode(file);
@@ -127,12 +137,13 @@ 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;

mm/hugetlb.c

+7 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#include <linux/bootmem.h>

#include <linux/sysfs.h>

#include <linux/slab.h>

#include <linux/mmdebug.h>

#include <linux/sched/signal.h>

#include <linux/rmap.h>

#include <linux/string_helpers.h>
@@ -4374,6 +4375,12 @@ 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