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Date:   Thu, 10 Sep 2020 13:37:49 +0530
From:   B K Karthik <bkkarthik@...u.pes.edu>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+72ff2fa98097767b5a27@...kaller.appspotmail.com>,
        Anant Thazhemadam <anant.thazhemadam@...il.com>,
        David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: KASAN: use-after-free Read in __xfrm6_tunnel_spi_lookup

On Thu, Sep 10, 2020 at 1:32 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Thu, Sep 10, 2020 at 9:20 AM Anant Thazhemadam
> <anant.thazhemadam@...il.com> wrote:
> > Looks like this bug is no longer valid. I'm not sure which commit seems to have fixed it. Can this be marked as invalid or closed yet?
>
> You can see on the dashboard (or in mailing list archives) that B K
> Karthik tested a patch for this bug in July:
> https://syzkaller.appspot.com/bug?extid=72ff2fa98097767b5a27
>
> So perhaps that patch fixes it? Karthik, did you send it? Was it
> merged? Did the commit include the syzbot Reported-by tag?
>

I did send it. I was taking a u32 spi value and casting it to a
pointer to an IP address. Steffen Klassert
<steffen.klassert@...unet.com> pointed out to me that the approach i
was looking at was completely wrong.
https://lkml.org/lkml/2020/7/27/361 is the conversation. hope this
helps.

thanks,

karthik
>
>
> On Thu, Jul 16, 2020 at 4:05 AM syzbot
> <syzbot+72ff2fa98097767b5a27@...kaller.appspotmail.com> wrote:
> >
> > syzbot has found a reproducer for the following issue on:
> >
> > HEAD commit:    ca0e494a Add linux-next specific files for 20200715
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=175099bf100000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2c76d72659687242
> > dashboard link: https://syzkaller.appspot.com/bug?extid=72ff2fa98097767b5a27
> > compiler:       gcc (GCC) 10.1.0-syz 20200507
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=112e8dbf100000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=109429bf100000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+72ff2fa98097767b5a27@...kaller.appspotmail.com
> >
> > netdevsim netdevsim0 netdevsim1: set [1, 0] type 2 family 0 port 6081 - 0
> > netdevsim netdevsim0 netdevsim2: set [1, 0] type 2 family 0 port 6081 - 0
> > netdevsim netdevsim0 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
> > ==================================================================
> > BUG: KASAN: use-after-free in __xfrm6_tunnel_spi_lookup+0x3a9/0x3b0 net/ipv6/xfrm6_tunnel.c:79
> > Read of size 8 at addr ffff8880934578a8 by task syz-executor437/6811
> > CPU: 0 PID: 6811 Comm: syz-executor437 Not tainted 5.8.0-rc5-next-20200715-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:77 [inline]
> >  dump_stack+0x18f/0x20d lib/dump_stack.c:118
> >  print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
> >  __kasan_report mm/kasan/report.c:513 [inline]
> >  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
> >  __xfrm6_tunnel_spi_lookup+0x3a9/0x3b0 net/ipv6/xfrm6_tunnel.c:79
> >  xfrm6_tunnel_spi_lookup+0x8a/0x1d0 net/ipv6/xfrm6_tunnel.c:95
> >  xfrmi6_rcv_tunnel+0xb9/0x100 net/xfrm/xfrm_interface.c:824
> >  tunnel6_rcv+0xef/0x2b0 net/ipv6/tunnel6.c:148
> >  ip6_protocol_deliver_rcu+0x2e8/0x1670 net/ipv6/ip6_input.c:433
> >  ip6_input_finish+0x7f/0x160 net/ipv6/ip6_input.c:474
> >  NF_HOOK include/linux/netfilter.h:307 [inline]
> >  NF_HOOK include/linux/netfilter.h:301 [inline]
> >  ip6_input+0x9c/0xd0 net/ipv6/ip6_input.c:483
> >  dst_input include/net/dst.h:449 [inline]
> >  ip6_rcv_finish net/ipv6/ip6_input.c:76 [inline]
> >  NF_HOOK include/linux/netfilter.h:307 [inline]
> >  NF_HOOK include/linux/netfilter.h:301 [inline]
> >  ipv6_rcv+0x28e/0x3c0 net/ipv6/ip6_input.c:307
> >  __netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5287
> >  __netif_receive_skb+0x27/0x1c0 net/core/dev.c:5401
> >  netif_receive_skb_internal net/core/dev.c:5503 [inline]
> >  netif_receive_skb+0x159/0x990 net/core/dev.c:5562
> >  tun_rx_batched.isra.0+0x460/0x720 drivers/net/tun.c:1518
> >  tun_get_user+0x23b2/0x35b0 drivers/net/tun.c:1972
> >  tun_chr_write_iter+0xba/0x151 drivers/net/tun.c:2001
> >  call_write_iter include/linux/fs.h:1879 [inline]
> >  new_sync_write+0x422/0x650 fs/read_write.c:515
> >  vfs_write+0x59d/0x6b0 fs/read_write.c:595
> >  ksys_write+0x12d/0x250 fs/read_write.c:648
> >  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > RIP: 0033:0x403d50
> > Code: Bad RIP value.
> > RSP: 002b:00007ffe8fe93368 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000403d50
> > RDX: 000000000000005e RSI: 00000000200007c0 RDI: 00000000000000f0
> > RBP: 00007ffe8fe93390 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe8fe93380
> > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> > Allocated by task 6811:
> >  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
> >  kasan_set_track mm/kasan/common.c:56 [inline]
> >  __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
> >  __do_kmalloc mm/slab.c:3655 [inline]
> >  __kmalloc+0x1a8/0x320 mm/slab.c:3664
> >  kmalloc include/linux/slab.h:559 [inline]
> >  kzalloc include/linux/slab.h:666 [inline]
> >  tomoyo_init_log+0x1335/0x1e50 security/tomoyo/audit.c:275
> >  tomoyo_supervisor+0x32f/0xeb0 security/tomoyo/common.c:2097
> >  tomoyo_audit_path_number_log security/tomoyo/file.c:235 [inline]
> >  tomoyo_path_number_perm+0x3ed/0x4d0 security/tomoyo/file.c:734
> >  security_file_ioctl+0x50/0xb0 security/security.c:1489
> >  ksys_ioctl+0x50/0x180 fs/ioctl.c:747
> >  __do_sys_ioctl fs/ioctl.c:762 [inline]
> >  __se_sys_ioctl fs/ioctl.c:760 [inline]
> >  __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
> >  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > Freed by task 6811:
> >  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
> >  kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
> >  kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355
> >  __kasan_slab_free+0xd8/0x120 mm/kasan/common.c:422
> >  __cache_free mm/slab.c:3418 [inline]
> >  kfree+0x103/0x2c0 mm/slab.c:3756
> >  tomoyo_supervisor+0x350/0xeb0 security/tomoyo/common.c:2149
> >  tomoyo_audit_path_number_log security/tomoyo/file.c:235 [inline]
> >  tomoyo_path_number_perm+0x3ed/0x4d0 security/tomoyo/file.c:734
> >  security_file_ioctl+0x50/0xb0 security/security.c:1489
> >  ksys_ioctl+0x50/0x180 fs/ioctl.c:747
> >  __do_sys_ioctl fs/ioctl.c:762 [inline]
> >  __se_sys_ioctl fs/ioctl.c:760 [inline]
> >  __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
> >  do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > The buggy address belongs to the object at ffff888093457800
> >  which belongs to the cache kmalloc-512 of size 512
> > The buggy address is located 168 bytes inside of
> >  512-byte region [ffff888093457800, ffff888093457a00)
> > The buggy address belongs to the page:
> > page:000000005c2b5911 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x93457
> > flags: 0xfffe0000000200(slab)
> > raw: 00fffe0000000200 ffffea00028d4308 ffffea0002834c88 ffff8880aa000600
> > raw: 0000000000000000 ffff888093457000 0000000100000004 0000000000000000
> > page dumped because: kasan: bad access detected
> > Memory state around the buggy address:
> >  ffff888093457780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >  ffff888093457800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > >ffff888093457880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >                                   ^
> >  ffff888093457900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >  ffff888093457980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ==================================================================

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