On 03/07/2018 05:35 PM, Yisheng Xie wrote: > Hi Mike, > > On 2018/3/8 7:59, 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. >> >> Reported-by: Nic Losby <blurbdust@xxxxxxxxx> >> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> >> --- >> fs/hugetlbfs/inode.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >> index 8fe1b0aa2896..cb288dec5564 100644 >> --- a/fs/hugetlbfs/inode.c >> +++ b/fs/hugetlbfs/inode.c >> @@ -127,12 +127,13 @@ 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 && ((loff_t)vma->vm_pgoff << PAGE_SHIFT) <= 0) >> return -EINVAL; > > This seems still no the right fix, taking the following case as an example: > mmap(0x20a00000, 0x600000, 0, 0x66033, -1, 0); > remap_file_pages(0x20a00000, 0x600000, 0, 0x0020001000000000, 0); > > You should just check the highest PAGE_SHIFT+1 bits of pgoff in you want check > at this point, right? Yes, thank you! That would be the correct check and also much simpler. Something like, unsigned long ovfl_mask; ovfl_mask = (1UL << (PAGE_SHIFT + 1)) - 1; ovfl_mask <<= ((sizeof(unsigned long) * BITS_PER_BYTE) - (PAGE_SHIFT + 1)); if (vma->vm_pgoff & ovfl_mask) return -EINVAL; > However, region_chg makes me a litter puzzle that when its return value < 0, sometime > adds_in_progress is added like this case, while sometime it is not. so why not just > change at the beginning of region_chg ? > if (f > t) > return -EINVAL; If region_chg returns a value < 0, this indicates an error and adds_in_progress should not be incremented. In the case of this bug, region_chg was passed values where f > t. Of course, this should never happen. But, because it assumed f <= t, it returned a negative count needed huge page reservations. The calling code interpreted the negative value as an error and a subsequent region_add or region_abort. I am not opposed to adding the suggested "if (f > t)". However, the region tracking routines are simple helpers only used by the hugetlbfs code and the assumption is that they are being called correctly. As such, I would prefer to leave off the check. But, this is the second time they have been called incorrectly due to insufficient argument checking. If we do add this to region_chg, I would also add the check to all region_* routines for consistency. I will send out a V2 of this patch tomorrow with the corrected overflow checking and possibly checks added to the region_* routines. -- Mike Kravetz
