On Mon, Jul 28, 2014 at 02:00:45PM -0700, akpm@xxxxxxxxxxxxxxxxxxxx wrote: > > The patch titled > Subject: mm: don't allow fault_around_bytes to be 0 > has been added to the -mm tree. Its filename is > mm-dont-allow-fault_around_bytes-to-be-0.patch > > This patch should soon appear at > http://ozlabs.org/~akpm/mmots/broken-out/mm-dont-allow-fault_around_bytes-to-be-0.patch > and later at > http://ozlabs.org/~akpm/mmotm/broken-out/mm-dont-allow-fault_around_bytes-to-be-0.patch > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/SubmitChecklist when testing your code *** > > The -mm tree is included into linux-next and is updated > there every 3-4 working days > > ------------------------------------------------------ > From: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> > Subject: mm: don't allow fault_around_bytes to be 0 > > Sasha Levin triggered use-after-free when fuzzing using trinity and the > KASAN patchset: > > AddressSanitizer: use after free in do_read_fault.isra.40+0x3c2/0x510 at addr ffff88048a733110 > page:ffffea001229ccc0 count:0 mapcount:0 mapping: (null) index:0x0 > page flags: 0xafffff80008000(tail) > page dumped because: kasan error > CPU: 6 PID: 9262 Comm: trinity-c104 Not tainted 3.16.0-rc6-next-20140723-sasha-00047-g289342b-dirty #929 > 00000000000000fb 0000000000000000 ffffea001229ccc0 ffff88038ac0fb78 > ffffffffa5e40903 ffff88038ac0fc48 ffff88038ac0fc38 ffffffffa142acfc > 0000000000000001 ffff880509ff5aa8 ffff88038ac10038 ffff88038ac0fbb0 > Call Trace: > dump_stack (lib/dump_stack.c:52) > kasan_report_error (mm/kasan/report.c:98 mm/kasan/report.c:166) > ? debug_smp_processor_id (lib/smp_processor_id.c:57) > ? preempt_count_sub (kernel/sched/core.c:2606) > ? put_lock_stats.isra.13 (./arch/x86/include/asm/preempt.h:98 kernel/locking/lockdep.c:254) > ? do_read_fault.isra.40 (mm/memory.c:2784 mm/memory.c:2849 mm/memory.c:2898) > __asan_load8 (mm/kasan/kasan.c:364) > ? do_read_fault.isra.40 (mm/memory.c:2864 mm/memory.c:2898) > do_read_fault.isra.40 (mm/memory.c:2864 mm/memory.c:2898) > ? _raw_spin_unlock (./arch/x86/include/asm/preempt.h:98 include/linux/spinlock_api_smp.h:152 kernel/locking/spinlock.c:183) > ? __pte_alloc (mm/memory.c:598) > handle_mm_fault (mm/memory.c:3092 mm/memory.c:3225 mm/memory.c:3345 mm/memory.c:3374) > ? pud_huge (./arch/x86/include/asm/paravirt.h:611 arch/x86/mm/hugetlbpage.c:76) > __get_user_pages (mm/gup.c:286 mm/gup.c:478) > __mlock_vma_pages_range (mm/mlock.c:262) > __mm_populate (mm/mlock.c:710) > SyS_remap_file_pages (mm/mmap.c:2653 mm/mmap.c:2593) > tracesys (arch/x86/kernel/entry_64.S:541) > Read of size 8 by thread T9262: > Memory state around the buggy address: > ffff88048a732e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a732f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a732f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a733000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a733080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > >ffff88048a733100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ^ > ffff88048a733180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a733200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a733280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a733300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff88048a733380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > It looks like that pte pointer is invalid in do_fault_around(). > This could happen if fault_around_bytes is set to 0. > fault_around_pages() and fault_around_mask() calls rounddown_pow_of_to(fault_around_bytes) > The result of rounddown_pow_of_to is undefined if parameter == 0 > (in my environment it returns 0x8000000000000000). > > One way to fix this would be to return 0 from fault_around_pages() if fault_around_bytes == 0, > however this would add extra code on fault path. > > So let's just forbid to set fault_around_bytes to zero. > Fault around is not used if fault_around_pages() <= 1, so if anyone doesn't want to use > it, fault_around_bytes could be set to any value in range [1, 2*PAGE_SIZE - 1] > instead of 0. > > Fixes: a9b0f861("mm: nominate faultaround area in bytes rather than page order") > Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> > Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Dave Jones <davej@xxxxxxxxxx> > Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> [3.15.x] > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff -puN mm/memory.c~mm-dont-allow-fault_around_bytes-to-be-0 mm/memory.c > --- a/mm/memory.c~mm-dont-allow-fault_around_bytes-to-be-0 > +++ a/mm/memory.c > @@ -2784,7 +2784,7 @@ static int fault_around_bytes_get(void * > > static int fault_around_bytes_set(void *data, u64 val) > { > - if (val / PAGE_SIZE > PTRS_PER_PTE) > + if (!val || val / PAGE_SIZE > PTRS_PER_PTE) > return -EINVAL; > fault_around_bytes = val; > return 0; Andrew, why did you decide to take this patch? Other patch by Andrey looks better. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>