On 07/28/14 13:36, Kirill A. Shutemov wrote: > On Mon, Jul 28, 2014 at 11:43:20AM +0400, Andrey Ryabinin wrote: >> 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). > > Ouch. Good catch! > > Although, I'm not convinced that it caused the issue. Sasha, did you touch the > debugfs handle? >
I suppose trinity could change it, no? I've got the very same spew after setting fault_around_bytes to 0. >> 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. > >>From user point of view, 0 is perfectly fine. What about untested patch > below? > In case if we are not going to get rid of debugfs interface I would better keep faul_around_bytes always roundded down, like in following patch: >From f41b7777b29f06dc62f80526e5617cae82a38709 Mon Sep 17 00:00:00 2001 From: Andrey Ryabinin <[email protected]> Date: Mon, 28 Jul 2014 13:46:10 +0400 Subject: [PATCH] mm: debugfs: move rounddown_pow_of_two() out from do_fault path do_fault_around expects fault_around_bytes rounded down to nearest page order. Instead of calling rounddown_pow_of_two every time in fault_around_pages()/fault_around_mask() we could do round down when user changes fault_around_bytes via debugfs interface. This also fixes bug when user set fault_around_bytes to 0. Result of rounddown_pow_of_two(0) is not defined, therefore fault_around_bytes == 0 doesn't work without this patch. Let's set fault_around_bytes to PAGE_SIZE if user sets to something less than PAGE_SIZE Fixes: a9b0f861("mm: nominate faultaround area in bytes rather than page order") Signed-off-by: Andrey Ryabinin <[email protected]> Cc: <[email protected]> # 3.15.x --- mm/memory.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 7e8d820..e0c6fd6 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2758,20 +2758,16 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address, update_mmu_cache(vma, address, pte); } -static unsigned long fault_around_bytes = 65536; +static unsigned long fault_around_bytes = rounddown_pow_of_two(65536); -/* - * fault_around_pages() and fault_around_mask() round down fault_around_bytes - * to nearest page order. It's what do_fault_around() expects to see. - */ static inline unsigned long fault_around_pages(void) { - return rounddown_pow_of_two(fault_around_bytes) / PAGE_SIZE; + return fault_around_bytes >> PAGE_SHIFT; } static inline unsigned long fault_around_mask(void) { - return ~(rounddown_pow_of_two(fault_around_bytes) - 1) & PAGE_MASK; + return ~(fault_around_bytes - 1) & PAGE_MASK; } @@ -2782,11 +2778,18 @@ static int fault_around_bytes_get(void *data, u64 *val) return 0; } +/* + * fault_around_pages() and fault_around_mask() expects fault_around_bytes + * rounded down to nearest page order. It's what do_fault_around() expects to see. + */ static int fault_around_bytes_set(void *data, u64 val) { if (val / PAGE_SIZE > PTRS_PER_PTE) return -EINVAL; - fault_around_bytes = val; + if (val > PAGE_SIZE) + fault_around_bytes = rounddown_pow_of_two(val); + else + fault_around_bytes = PAGE_SIZE; /* rounddown_pow_of_two(0) is undefined */ return 0; } DEFINE_SIMPLE_ATTRIBUTE(fault_around_bytes_fops, -- 1.8.5.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
