Re: [PATCH] mm/hugetlb: Don't call region_abort if region_chg fails

[Hillf Danton]

Reply again with Andrew's mail address corrected:)

-'Andrew Morton' <akpm@linux^Coundation.org>
+'Andrew Morton' <akpm@xxxxxxxxxxxxxxxxxxxx>
> 
> On March 24, 2017 12:03 PM Mike Kravetz wrote:
> >
> > Changes to hugetlbfs reservation maps is a two step process.  The first
> > step is a call to region_chg to determine what needs to be changed, and
> > prepare that change.  This should be followed by a call to call to
> > region_add to commit the change, or region_abort to abort the change.
> >
> > The error path in hugetlb_reserve_pages called region_abort after a
> > failed call to region_chg.  As a result, the adds_in_progress counter
> > in the reservation map is off by 1.  This is caught by a VM_BUG_ON
> > in resv_map_release when the reservation map is freed.
> >
> > syzkaller fuzzer found this bug, that resulted in the following:
> >
> >  kernel BUG at mm/hugetlb.c:742!
> >  Call Trace:
> >   hugetlbfs_evict_inode+0x7b/0xa0 fs/hugetlbfs/inode.c:493
> >   evict+0x481/0x920 fs/inode.c:553
> >   iput_final fs/inode.c:1515 [inline]
> >   iput+0x62b/0xa20 fs/inode.c:1542
> >   hugetlb_file_setup+0x593/0x9f0 fs/hugetlbfs/inode.c:1306
> >   newseg+0x422/0xd30 ipc/shm.c:575
> >   ipcget_new ipc/util.c:285 [inline]
> >   ipcget+0x21e/0x580 ipc/util.c:639
> >   SYSC_shmget ipc/shm.c:673 [inline]
> >   SyS_shmget+0x158/0x230 ipc/shm.c:657
> >   entry_SYSCALL_64_fastpath+0x1f/0xc2
> >  RIP: resv_map_release+0x265/0x330 mm/hugetlb.c:742
> >
> > Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > ---
> 
> Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> 
> >  mm/hugetlb.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index c7025c1..c65d45c 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -4233,7 +4233,9 @@ int hugetlb_reserve_pages(struct inode *inode,
> >  	return 0;
> >  out_err:
> >  	if (!vma || vma->vm_flags & VM_MAYSHARE)
> > -		region_abort(resv_map, from, to);
> > +		/* Don't call region_abort if region_chg failed */
> > +		if (chg >= 0)
> > +			region_abort(resv_map, from, to);
> >  	if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
> >  		kref_put(&resv_map->refs, resv_map_release);
> >  	return ret;
> > --
> > 2.7.4