Re: [PATCH] mm: fix racing of vb->va when kasan enabled

[Uladzislau Rezki]

> On Thu, May 26, 2022 at 10:18 AM zhaoyang.huang
> <zhaoyang.huang@xxxxxxxxxx> wrote:
> >
> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> >
> > Accessing to vb->va could be deemed as use after free when KASAN is
> > enabled like bellowing. Fix it by expanding the mutex's range.
> >
> > [   20.232335] ==================================================================
> > [   20.232365] BUG: KASAN: use-after-free in _vm_unmap_aliases+0x164/0x364
> > [   20.232376] Read of size 8 at addr ffffff80d84af780 by task modprobe/300
> > [   20.232380]
> > [   20.232395] CPU: 5 PID: 300 Comm: modprobe Tainted: G S       C O      5.4.161-android12-9-03238-gd43329d103de-ab20547 #1
> > [   20.232401] Hardware name: Spreadtrum UMS512-1H10 SoC (DT)
> > [   20.232407] Call trace:
> > [   20.232419]  dump_backtrace+0x0/0x2b4
> > [   20.232428]  show_stack+0x24/0x30
> > [   20.232443]  dump_stack+0x15c/0x1f4
> > [   20.232455]  print_address_description+0x88/0x568
> > [   20.232465]  __kasan_report+0x1b8/0x1dc
> > [   20.232474]  kasan_report+0x10/0x18
> > [   20.232486]  __asan_report_load8_noabort+0x1c/0x24
> > [   20.232495]  _vm_unmap_aliases+0x164/0x364
> > [   20.232505]  vm_unmap_aliases+0x20/0x28
> > [   20.232516]  change_memory_common+0x2c4/0x3ec
> > [   20.232524]  set_memory_ro+0x30/0x3c
> > [   20.232539]  module_enable_ro+0x144/0x3f0
> > [   20.232547]  load_module+0x54c0/0x8248
> > [   20.232555]  __se_sys_finit_module+0x174/0x1b0
> > [   20.232564]  __arm64_sys_finit_module+0x78/0x88
> > [   20.232573]  el0_svc_common+0x19c/0x354
> > [   20.232581]  el0_svc_handler+0x48/0x54
> > [   20.232591]  el0_svc+0x8/0xc
> > [   20.232595]
> > [   20.232602] Allocated by task 297:
> > [   20.232615]  __kasan_kmalloc+0x130/0x1f8
> > [   20.232625]  kasan_slab_alloc+0x14/0x1c
> > [   20.232638]  kmem_cache_alloc+0x1dc/0x394
> > [   20.232648]  alloc_vmap_area+0xb4/0x1630
> > [   20.232657]  vm_map_ram+0x3ac/0x768
> > [   20.232671]  z_erofs_decompress_generic+0x2f0/0x844
> > [   20.232681]  z_erofs_decompress+0xa8/0x594
> > [   20.232692]  z_erofs_decompress_pcluster+0xeb4/0x1458
> > [   20.232702]  z_erofs_vle_unzip_wq+0xe4/0x140
> > [   20.232715]  process_one_work+0x5c0/0x10ac
> > [   20.232724]  worker_thread+0x888/0x1128
> > [   20.232733]  kthread+0x290/0x304
> > [   20.232744]  ret_from_fork+0x10/0x18
> > [   20.232747]
> > [   20.232752] Freed by task 51:
> > [   20.232762]  __kasan_slab_free+0x1a0/0x270
> > [   20.232772]  kasan_slab_free+0x10/0x1c
> > [   20.232781]  slab_free_freelist_hook+0xd0/0x1ac
> > [   20.232792]  kmem_cache_free+0x110/0x368
> > [   20.232803]  __purge_vmap_area_lazy+0x524/0x13e4
> > [   20.232813]  _vm_unmap_aliases+0x290/0x364
> > [   20.232822]  __vunmap+0x45c/0x5c4
> > [   20.232831]  vfree+0x74/0x16c
> > [   20.232841]  module_memfree+0x44/0x7c
> > [   20.232850]  do_free_init+0x5c/0xac
> > [   20.232860]  process_one_work+0x5c0/0x10ac
> > [   20.232869]  worker_thread+0xb3c/0x1128
> > [   20.232877]  kthread+0x290/0x304
> > [   20.232887]  ret_from_fork+0x10/0x18
> >
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> >  mm/vmalloc.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index d2a00ad..028d65a 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2081,7 +2081,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
> >                 return;
> >
> >         might_sleep();
> > -
> > +       mutex_lock(&vmap_purge_lock);
> >         for_each_possible_cpu(cpu) {
> >                 struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, cpu);
> >                 struct vmap_block *vb;
> > @@ -2106,7 +2106,6 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
> >                 rcu_read_unlock();
> >         }
> >
> > -       mutex_lock(&vmap_purge_lock);
> >         purge_fragmented_blocks_allcpus();
> >         if (!__purge_vmap_area_lazy(start, end) && flush)
> >                 flush_tlb_kernel_range(start, end);
> > --
> > 1.9.1
> >
>
Is it easy to reproduce? If so could you please describe the steps? As i see
the freeing of the "vb" is RCU safe whereas vb->va is not. But from the first
glance i do not see how it can accessed twice. Hm..

--
Uladzislau Rezki