Re: [syzbot] [mm?] KASAN: slab-use-after-free Read in hugetlb_fault (2)

[Vishal Moola <vishal.moola@gmail.com>]

On Mon, Sep 09, 2024 at 05:57:52PM +0800, Muchun Song wrote:
> 
> 
> > On Sep 9, 2024, at 02:23, syzbot <syzbot+2dab93857ee95f2eeb08@syzkaller.appspotmail.com> wrote:
> > 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    88fac17500f4 Merge tag 'fuse-fixes-6.11-rc7' of git://git...
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13291d97980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=660f6eb11f9c7dc5
> > dashboard link: https://syzkaller.appspot.com/bug?extid=2dab93857ee95f2eeb08
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > 
> > Unfortunately, I don't have any reproducer for this issue yet.
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/6dfa1c637f53/disk-88fac175.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/7a322b491698/vmlinux-88fac175.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/edc9184a3a97/bzImage-88fac175.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+2dab93857ee95f2eeb08@syzkaller.appspotmail.com
> > 
> > ==================================================================
> > BUG: KASAN: slab-use-after-free in __vma_shareable_lock include/linux/hugetlb.h:1278 [inline]
> 
> This is accessing vma structure.
> 
> > BUG: KASAN: slab-use-after-free in hugetlb_vma_unlock_read mm/hugetlb.c:281 [inline]
> > BUG: KASAN: slab-use-after-free in hugetlb_no_page mm/hugetlb.c:6380 [inline]
> > BUG: KASAN: slab-use-after-free in hugetlb_fault+0xfaf/0x3770 mm/hugetlb.c:6485
> > Read of size 8 at addr ffff88807c17f9d0 by task syz.0.4558/26998
> > 
> > CPU: 1 UID: 0 PID: 26998 Comm: syz.0.4558 Not tainted 6.11.0-rc6-syzkaller-00026-g88fac17500f4 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
> > Call Trace:
> > <TASK>
> > __dump_stack lib/dump_stack.c:93 [inline]
> > dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
> > print_address_description mm/kasan/report.c:377 [inline]
> > print_report+0x169/0x550 mm/kasan/report.c:488
> > kasan_report+0x143/0x180 mm/kasan/report.c:601
> > __vma_shareable_lock include/linux/hugetlb.h:1278 [inline]
> > hugetlb_vma_unlock_read mm/hugetlb.c:281 [inline]
> 
> I think vma is freed before this call of hugetlb_vma_unlock_read()
> but after hugetlb_vma_lock_read() in hugetlb_fault(). I found a
> possible scenario to cause this problem.
> 
> hugetlb_no_page()
> 	ret = vmf_anon_prepare()
> 		if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> 			if (!mmap_read_trylock(vma->vm_mm)) {
> 				vma_end_read(vma);
> 				// VMA lock is released, which could be freed before the call of hugetlb_vma_unlock_read().
> 				return VM_FAULT_RETRY;
> 			}
> 		}
> 	if (unlikely(ret))
> 		goto out;
> out:
> 	hugetlb_vma_unlock_read(vma); // UAF of VMA

Thanks for catching this, it indeed looks like the problem. I don't
think its easy to reproduce since we would have to unmap the vma while
a fault is being handled (and failing).

This same issue should be present in hugetlb_wp() as well, so I'm thinking
the best fix would be to make another function similar to
vmf_anon_prepare() that doesn't release the vma lock. Then wait to drop
the lock until hugetlb_vma_unlock_read() is called.

I'll have that fix out tomorrow.

> The culprit commit should be
> 	
> 	7c43a553792a1 ("hugetlb: allow faults to be handled under the VMA lock").
> 
> I will take a closer look at the solution tomorrow. And Cc the author of the
> above commit, maybe have some comments on this.
> 
> Muchun,
> Thanks.
> 
> > hugetlb_no_page mm/hugetlb.c:6380 [inline]
> > hugetlb_fault+0xfaf/0x3770 mm/hugetlb.c:6485
> > handle_mm_fault+0x1901/0x1bc0 mm/memory.c:5830
> > do_user_addr_fault arch/x86/mm/fault.c:1338 [inline]
> > handle_page_fault arch/x86/mm/fault.c:1481 [inline]
> > exc_page_fault+0x459/0x8c0 arch/x86/mm/fault.c:1539
> > asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
> > RIP: 0033:0x7f2b63744998
> > Code: fc 89 37 c3 c5 fa 6f 06 c5 fa 6f 4c 16 f0 c5 fa 7f 07 c5 fa 7f 4c 17 f0 c3 66 0f 1f 84 00 00 00 00 00 48 8b 4c 16 f8 48 8b 36 <48> 89 37 48 89 4c 17 f8 c3 c5 fe 6f 54 16 e0 c5 fe 6f 5c 16 c0 c5
> > RSP: 002b:00007f2b63a5fb88 EFLAGS: 00010206
> > RAX: 00000000200002c0 RBX: 0000000000000004 RCX: 00676e7277682f76
> > RDX: 000000000000000b RSI: 7277682f7665642f RDI: 00000000200002c0
> > RBP: 00007f2b63937a80 R08: 00007f2b63600000 R09: 0000000000000001
> > R10: 0000000000000001 R11: 0000000000000009 R12: 000000000014aa5e
> > R13: 00007f2b63a5fc90 R14: 0000000000000032 R15: fffffffffffffffe
> > </TASK>
> > 
> > Allocated by task 27000:
> > kasan_save_stack mm/kasan/common.c:47 [inline]
> > kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
> > unpoison_slab_object mm/kasan/common.c:312 [inline]
> > __kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:338
> > kasan_slab_alloc include/linux/kasan.h:201 [inline]
> > slab_post_alloc_hook mm/slub.c:3988 [inline]
> > slab_alloc_node mm/slub.c:4037 [inline]
> > kmem_cache_alloc_noprof+0x135/0x2a0 mm/slub.c:4044
> > vm_area_alloc+0x24/0x1d0 kernel/fork.c:471
> > mmap_region+0xc3d/0x2090 mm/mmap.c:2944
> > do_mmap+0x8f9/0x1010 mm/mmap.c:1468
> > vm_mmap_pgoff+0x1dd/0x3d0 mm/util.c:588
> > ksys_mmap_pgoff+0x544/0x720 mm/mmap.c:1514
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > 
> > Freed by task 26255:
> > kasan_save_stack mm/kasan/common.c:47 [inline]
> > kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
> > kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579
> > poison_slab_object+0xe0/0x150 mm/kasan/common.c:240
> > __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256
> > kasan_slab_free include/linux/kasan.h:184 [inline]
> > slab_free_hook mm/slub.c:2252 [inline]
> > slab_free mm/slub.c:4473 [inline]
> > kmem_cache_free+0x145/0x350 mm/slub.c:4548
> > rcu_do_batch kernel/rcu/tree.c:2569 [inline]
> > rcu_core+0xafd/0x1830 kernel/rcu/tree.c:2843
> 
> VMA structure is freed via rcu, so it is really a UAF problem.
> 
> > handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
> > do_softirq+0x11b/0x1e0 kernel/softirq.c:455
> > __local_bh_enable_ip+0x1bb/0x200 kernel/softirq.c:382
> > spin_unlock_bh include/linux/spinlock.h:396 [inline]
> > __fib6_clean_all+0x327/0x4b0 net/ipv6/ip6_fib.c:2277
> > rt6_sync_down_dev net/ipv6/route.c:4908 [inline]
> > rt6_disable_ip+0x164/0x7e0 net/ipv6/route.c:4913
> > addrconf_ifdown+0x15d/0x1bd0 net/ipv6/addrconf.c:3856
> > addrconf_notify+0x3cb/0x1020
> > notifier_call_chain+0x19f/0x3e0 kernel/notifier.c:93
> > call_netdevice_notifiers_extack net/core/dev.c:2032 [inline]
> > call_netdevice_notifiers net/core/dev.c:2046 [inline]
> > dev_close_many+0x33c/0x4c0 net/core/dev.c:1587
> > unregister_netdevice_many_notify+0x50b/0x1c40 net/core/dev.c:11327
> > unregister_netdevice_many net/core/dev.c:11414 [inline]
> > default_device_exit_batch+0xa0f/0xa90 net/core/dev.c:11897
> > ops_exit_list net/core/net_namespace.c:178 [inline]
> > cleanup_net+0x89d/0xcc0 net/core/net_namespace.c:640
> > process_one_work kernel/workqueue.c:3231 [inline]
> > process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
> > worker_thread+0x86d/0xd10 kernel/workqueue.c:3389
> > kthread+0x2f0/0x390 kernel/kthread.c:389
> > ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> > 
> > Last potentially related work creation:
> > kasan_save_stack+0x3f/0x60 mm/kasan/common.c:47
> > __kasan_record_aux_stack+0xac/0xc0 mm/kasan/generic.c:541
> > __call_rcu_common kernel/rcu/tree.c:3106 [inline]
> > call_rcu+0x167/0xa70 kernel/rcu/tree.c:3210
> > remove_vma mm/mmap.c:189 [inline]
> > remove_mt mm/mmap.c:2415 [inline]
> > do_vmi_align_munmap+0x155c/0x18c0 mm/mmap.c:2758
> > do_vmi_munmap+0x261/0x2f0 mm/mmap.c:2830
> > mmap_region+0x72f/0x2090 mm/mmap.c:2881
> > do_mmap+0x8f9/0x1010 mm/mmap.c:1468
> > vm_mmap_pgoff+0x1dd/0x3d0 mm/util.c:588
> > ksys_mmap_pgoff+0x544/0x720 mm/mmap.c:1514
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > 
> > The buggy address belongs to the object at ffff88807c17f9b0
> > which belongs to the cache vm_area_struct of size 184
> > The buggy address is located 32 bytes inside of
> > freed 184-byte region [ffff88807c17f9b0, ffff88807c17fa68)
> > 
> > The buggy address belongs to the physical page:
> > page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7c17f
> > memcg:ffff888028997401
> > anon flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
> > page_type: 0xfdffffff(slab)
> > raw: 00fff00000000000 ffff88801bafdb40 ffffea0001f89e00 000000000000000d
> > raw: 0000000000000000 0000000000100010 00000001fdffffff ffff888028997401
> > page dumped because: kasan: bad access detected
> > page_owner tracks the page as allocated
> > page last allocated via order 0, migratetype Unmovable, gfp_mask 0x152cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 26741, tgid 26741 (dhcpcd-run-hook), ts 1341391347767, free_ts 1341166373745
> > set_page_owner include/linux/page_owner.h:32 [inline]
> > post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1493
> > prep_new_page mm/page_alloc.c:1501 [inline]
> > get_page_from_freelist+0x2e4c/0x2f10 mm/page_alloc.c:3439
> > __alloc_pages_noprof+0x256/0x6c0 mm/page_alloc.c:4695
> > __alloc_pages_node_noprof include/linux/gfp.h:269 [inline]
> > alloc_pages_node_noprof include/linux/gfp.h:296 [inline]
> > alloc_slab_page+0x5f/0x120 mm/slub.c:2321
> > allocate_slab+0x5a/0x2f0 mm/slub.c:2484
> > new_slab mm/slub.c:2537 [inline]
> > ___slab_alloc+0xcd1/0x14b0 mm/slub.c:3723
> > __slab_alloc+0x58/0xa0 mm/slub.c:3813
> > __slab_alloc_node mm/slub.c:3866 [inline]
> > slab_alloc_node mm/slub.c:4025 [inline]
> > kmem_cache_alloc_noprof+0x1c1/0x2a0 mm/slub.c:4044
> > vm_area_dup+0x27/0x290 kernel/fork.c:486
> > dup_mmap kernel/fork.c:695 [inline]
> > dup_mm kernel/fork.c:1672 [inline]
> > copy_mm+0xc7b/0x1f30 kernel/fork.c:1721
> > copy_process+0x187a/0x3dc0 kernel/fork.c:2374
> > kernel_clone+0x226/0x8f0 kernel/fork.c:2781
> > __do_sys_clone kernel/fork.c:2924 [inline]
> > __se_sys_clone kernel/fork.c:2908 [inline]
> > __x64_sys_clone+0x258/0x2a0 kernel/fork.c:2908
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > page last free pid 26730 tgid 26718 stack trace:
> > reset_page_owner include/linux/page_owner.h:25 [inline]
> > free_pages_prepare mm/page_alloc.c:1094 [inline]
> > free_unref_page+0xd22/0xea0 mm/page_alloc.c:2612
> > __folio_put+0x2c8/0x440 mm/swap.c:128
> > migrate_folio_move mm/migrate.c:1330 [inline]
> > migrate_pages_batch+0x2a76/0x3560 mm/migrate.c:1818
> > migrate_pages_sync mm/migrate.c:1884 [inline]
> > migrate_pages+0x1f59/0x3460 mm/migrate.c:1993
> > do_mbind mm/mempolicy.c:1388 [inline]
> > kernel_mbind mm/mempolicy.c:1531 [inline]
> > __do_sys_mbind mm/mempolicy.c:1605 [inline]
> > __se_sys_mbind+0x1490/0x19f0 mm/mempolicy.c:1601
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > 
> > Memory state around the buggy address:
> > ffff88807c17f880: fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00 00
> > ffff88807c17f900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
> >> ffff88807c17f980: fc fc fc fc fc fc fa fb fb fb fb fb fb fb fb fb
> >                                                 ^
> > ffff88807c17fa00: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc
> > ffff88807c17fa80: fc fc fc fc fc 00 00 00 00 00 00 00 00 00 00 00
> > ==================================================================
> > 
> > 
> > ---
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> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > 
> > syzbot will keep track of this issue. See:
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> > 
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> > 
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> > 
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> > 
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>