On Thu, 8 Mar 2018 16:27:26 -0800 Mike Kravetz mike.kravetz@oracle.com 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.
...
--- 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;- }
This is tidier, and that comment is a bit too obvious to live ;)
--- a/mm/hugetlb.c~hugetlbfs-check-for-pgoff-value-overflow-v3-fix +++ a/mm/hugetlb.c @@ -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> @@ -4374,11 +4375,8 @@ int hugetlb_reserve_pages(struct 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__); + if (VM_WARN(from > to, "%s called with a negative range\n", __func__)) return -EINVAL; - }
/* * Only apply hugepage reservation if asked. At fault time, an