Message-ID: <CABBYNZJjot3_2u61Uo3mT3b-K9i9uQgQ1B0N1=42nOFDf22OFw@mail.gmail.com>
Date:   Thu, 7 Oct 2021 17:26:13 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzbot+2bef95d3ab4daa10155b@...kaller.appspotmail.com,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [RESEND PATCH] Bluetooth: fix race in sco_sock_connect

Hi Desmond.

On Mon, Oct 4, 2021 at 11:02 AM Desmond Cheong Zhi Xi
<desmondcheongzx@...il.com> wrote:
>
> Syzbot reported a use-after-free Write in sco_sock_timeout [1]:
>
> ==================================================================
> BUG: KASAN: use-after-free in instrument_atomic_read_write
> include/linux/instrumented.h:101 [inline]
> BUG: KASAN: use-after-free in atomic_fetch_add_relaxed
> include/asm-generic/atomic-instrumented.h:111 [inline]
> BUG: KASAN: use-after-free in __refcount_add
> include/linux/refcount.h:193 [inline]
> BUG: KASAN: use-after-free in __refcount_inc
> include/linux/refcount.h:250 [inline]
> BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
> BUG: KASAN: use-after-free in sock_hold include/net/sock.h:702 [inline]
> BUG: KASAN: use-after-free in sco_sock_timeout+0x64/0x290 net/bluetooth/sco.c:88
> Write of size 4 at addr ffff888034b46080 by task kworker/1:0/20
>
> CPU: 1 PID: 20 Comm: kworker/1:0 Not tainted 5.14.0-rc6-syzkaller #0
> Workqueue: events sco_sock_timeout
> Call Trace:
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
>  print_address_description.constprop.0.cold+0x6c/0x309 mm/kasan/report.c:233
>  __kasan_report mm/kasan/report.c:419 [inline]
>  kasan_report.cold+0x83/0xdf mm/kasan/report.c:436
>  check_region_inline mm/kasan/generic.c:183 [inline]
>  kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
>  instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
>  atomic_fetch_add_relaxed include/asm-generic/atomic-instrumented.h:111 [inline]
>  __refcount_add include/linux/refcount.h:193 [inline]
>  __refcount_inc include/linux/refcount.h:250 [inline]
>  refcount_inc include/linux/refcount.h:267 [inline]
>  sock_hold include/net/sock.h:702 [inline]
>  sco_sock_timeout+0x64/0x290 net/bluetooth/sco.c:88
>  process_one_work+0x98d/0x1630 kernel/workqueue.c:2276
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2422
>  kthread+0x3e5/0x4d0 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
>
> Allocated by task 4872:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:434 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:513 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:472 [inline]
>  __kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:522
>  kmalloc include/linux/slab.h:596 [inline]
>  sk_prot_alloc+0x110/0x290 net/core/sock.c:1822
>  sk_alloc+0x32/0xbc0 net/core/sock.c:1875
>  __netlink_create+0x63/0x2f0 net/netlink/af_netlink.c:640
>  netlink_create+0x3ad/0x5e0 net/netlink/af_netlink.c:703
>  __sock_create+0x353/0x790 net/socket.c:1461
>  sock_create net/socket.c:1512 [inline]
>  __sys_socket+0xef/0x200 net/socket.c:1554
>  __do_sys_socket net/socket.c:1563 [inline]
>  __se_sys_socket net/socket.c:1561 [inline]
>  __x64_sys_socket+0x6f/0xb0 net/socket.c:1561
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Freed by task 0:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
>  kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:360
>  ____kasan_slab_free mm/kasan/common.c:366 [inline]
>  ____kasan_slab_free mm/kasan/common.c:328 [inline]
>  __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:374
>  kasan_slab_free include/linux/kasan.h:230 [inline]
>  slab_free_hook mm/slub.c:1628 [inline]
>  slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1653
>  slab_free mm/slub.c:3213 [inline]
>  kfree+0xe4/0x540 mm/slub.c:4267
>  sk_prot_free net/core/sock.c:1858 [inline]
>  __sk_destruct+0x6a8/0x900 net/core/sock.c:1943
>  sk_destruct+0xbd/0xe0 net/core/sock.c:1958
>  __sk_free+0xef/0x3d0 net/core/sock.c:1969
>  sk_free+0x78/0xa0 net/core/sock.c:1980
>  deferred_put_nlk_sk+0x151/0x2f0 net/netlink/af_netlink.c:740
>  rcu_do_batch kernel/rcu/tree.c:2550 [inline]
>  rcu_core+0x7ab/0x1380 kernel/rcu/tree.c:2785
>  __do_softirq+0x29b/0x9c2 kernel/softirq.c:558
>
> Last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:348
>  __call_rcu kernel/rcu/tree.c:3029 [inline]
>  call_rcu+0xb1/0x750 kernel/rcu/tree.c:3109
>  netlink_release+0xdd4/0x1dd0 net/netlink/af_netlink.c:812
>  __sock_release+0xcd/0x280 net/socket.c:649
>  sock_close+0x18/0x20 net/socket.c:1311
>  __fput+0x288/0x920 fs/file_table.c:280
>  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>  exit_task_work include/linux/task_work.h:32 [inline]
>  do_exit+0xbd4/0x2a60 kernel/exit.c:825
>  do_group_exit+0x125/0x310 kernel/exit.c:922
>  __do_sys_exit_group kernel/exit.c:933 [inline]
>  __se_sys_exit_group kernel/exit.c:931 [inline]
>  __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:931
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Second to last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:348
>  __call_rcu kernel/rcu/tree.c:3029 [inline]
>  call_rcu+0xb1/0x750 kernel/rcu/tree.c:3109
>  netlink_release+0xdd4/0x1dd0 net/netlink/af_netlink.c:812
>  __sock_release+0xcd/0x280 net/socket.c:649
>  sock_close+0x18/0x20 net/socket.c:1311
>  __fput+0x288/0x920 fs/file_table.c:280
>  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>  exit_task_work include/linux/task_work.h:32 [inline]
>  do_exit+0xbd4/0x2a60 kernel/exit.c:825
>  do_group_exit+0x125/0x310 kernel/exit.c:922
>  __do_sys_exit_group kernel/exit.c:933 [inline]
>  __se_sys_exit_group kernel/exit.c:931 [inline]
>  __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:931
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The buggy address belongs to the object at ffff888034b46000
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 128 bytes inside of
>  2048-byte region [ffff888034b46000, ffff888034b46800)
> The buggy address belongs to the page:
> page:ffffea0000d2d000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x34b40
> head:ffffea0000d2d000 order:3 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000010200 ffffea0000c37a00 0000000200000002 ffff888010c42000
> raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 8634, ts 417197903424, free_ts 417180376519
>  prep_new_page mm/page_alloc.c:2436 [inline]
>  get_page_from_freelist+0xa72/0x2f80 mm/page_alloc.c:4169
>  __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5391
>  alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2244
>  alloc_slab_page mm/slub.c:1691 [inline]
>  allocate_slab+0x32e/0x4b0 mm/slub.c:1831
>  new_slab mm/slub.c:1894 [inline]
>  new_slab_objects mm/slub.c:2640 [inline]
>  ___slab_alloc+0x473/0x7b0 mm/slub.c:2803
>  __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2843
>  slab_alloc_node mm/slub.c:2925 [inline]
>  __kmalloc_node_track_caller+0x2e3/0x360 mm/slub.c:4653
>  kmalloc_reserve net/core/skbuff.c:355 [inline]
>  __alloc_skb+0xde/0x340 net/core/skbuff.c:426
>  alloc_skb include/linux/skbuff.h:1116 [inline]
>  alloc_skb_with_frags+0x93/0x620 net/core/skbuff.c:6073
>  sock_alloc_send_pskb+0x783/0x910 net/core/sock.c:2475
>  mld_newpack+0x1df/0x770 net/ipv6/mcast.c:1756
>  add_grhead+0x265/0x330 net/ipv6/mcast.c:1859
>  add_grec+0x1053/0x14e0 net/ipv6/mcast.c:1997
>  mld_send_initial_cr.part.0+0xf6/0x230 net/ipv6/mcast.c:2244
>  mld_send_initial_cr net/ipv6/mcast.c:1232 [inline]
>  ipv6_mc_dad_complete+0x1d0/0x690 net/ipv6/mcast.c:2255
>  addrconf_dad_completed+0xa20/0xd60 net/ipv6/addrconf.c:4181
> page last free stack trace:
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1346 [inline]
>  free_pcp_prepare+0x2c5/0x780 mm/page_alloc.c:1397
>  free_unref_page_prepare mm/page_alloc.c:3332 [inline]
>  free_unref_page+0x19/0x690 mm/page_alloc.c:3411
>  unfreeze_partials+0x16c/0x1b0 mm/slub.c:2421
>  put_cpu_partial+0x13d/0x230 mm/slub.c:2457
>  qlink_free mm/kasan/quarantine.c:146 [inline]
>  qlist_free_all+0x5a/0xc0 mm/kasan/quarantine.c:165
>  kasan_quarantine_reduce+0x180/0x200 mm/kasan/quarantine.c:272
>  __kasan_slab_alloc+0x8e/0xa0 mm/kasan/common.c:444
>  kasan_slab_alloc include/linux/kasan.h:254 [inline]
>  slab_post_alloc_hook mm/slab.h:519 [inline]
>  slab_alloc_node mm/slub.c:2959 [inline]
>  slab_alloc mm/slub.c:2967 [inline]
>  kmem_cache_alloc+0x285/0x4a0 mm/slub.c:2972
>  getname_flags.part.0+0x50/0x4f0 fs/namei.c:138
>  getname_flags fs/namei.c:2747 [inline]
>  user_path_at_empty+0xa1/0x100 fs/namei.c:2747
>  user_path_at include/linux/namei.h:57 [inline]
>  vfs_statx+0x142/0x390 fs/stat.c:203
>  vfs_fstatat fs/stat.c:225 [inline]
>  vfs_lstat include/linux/fs.h:3386 [inline]
>  __do_sys_newlstat+0x91/0x110 fs/stat.c:380
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Memory state around the buggy address:
>  ffff888034b45f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888034b46000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff888034b46080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                    ^
>  ffff888034b46100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888034b46180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> sco_sock_connect checks the socket's state before allocating a new SCO
> connection and creating a channel for it with the given socket.
>
> However, because this check occurs outside the socket lock, multiple
> concurrent calls to sco_sock_connect are able to pass the check before
> serially entering the critical section and making multiple recursive
> calls to sco_connect.
>
> The result is that multiple SCO connections are allocated, but each
> connection overrides the socket's channel with the previous
> connection. This may cause a UAF because the overwritten connections
> can't have their channels deleted when the socket is released, so
> sco_sock_timeout is able to access the freed socket.
>
> Fix this by checking the socket's state after the socket is locked in
> sco_sock_connect.
>
> Link: https://syzkaller.appspot.com/bug?extid=2bef95d3ab4daa10155b [1]
> Reported-by: syzbot+2bef95d3ab4daa10155b@...kaller.appspotmail.com
> Tested-by: syzbot+2bef95d3ab4daa10155b@...kaller.appspotmail.com
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
> Cc: Hillf Danton <hdanton@...a.com>
> ---
>
> Hi Maintainers,
>
> Resending this patch because the bug is still being hit regularly by
> Syzbot. Thoughts would be very appreciated.
>
> Best wishes,
> Desmond
>
>  net/bluetooth/sco.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
> index 8eabf41b2993..e6a9e9e6e795 100644
> --- a/net/bluetooth/sco.c
> +++ b/net/bluetooth/sco.c
> @@ -574,9 +574,6 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
>             addr->sa_family != AF_BLUETOOTH)
>                 return -EINVAL;
>
> -       if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND)
> -               return -EBADFD;
> -
>         if (sk->sk_type != SOCK_SEQPACKET)
>                 return -EINVAL;
>
> @@ -587,6 +584,13 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr *addr, int alen
>
>         lock_sock(sk);
>
> +       if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
> +               hci_dev_unlock(hdev);
> +               hci_dev_put(hdev);
> +               err = -EBADFD;
> +               goto done;
> +       }

So this is getting really messy, first we have the locking dependency
so we had to do hci_dev_lock before sock_lock and now we have to move
back the checks since it really needs lock_sock anyway, it really
sounds like we are back and forth with this. Also from the description
I assume sco_add_chan is the problem since sco_conn is create during
the syscall we can't actually use its lock to serialize the requests,
so I wonder if it wouldn't be better to do something like l2cap_sock.c
does, have the data created on sock_create so we can use conn->sock in
sco_conn_add.

>         /* Set destination address and psm */
>         bacpy(&sco_pi(sk)->dst, &sa->sco_bdaddr);
>
> --
> 2.25.1
>


-- 
Luiz Augusto von Dentz

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