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    Subject[PATCH 4.14 06/45] neigh: fix use-after-free read in pneigh_get_next
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit f3e92cb8e2eb8c27d109e6fd73d3a69a8c09e288 ]

    Nine years ago, I added RCU handling to neighbours, not pneighbours.
    (pneigh are not commonly used)

    Unfortunately I missed that /proc dump operations would use a
    common entry and exit point : neigh_seq_start() and neigh_seq_stop()

    We need to read_lock(tbl->lock) or risk use-after-free while
    iterating the pneigh structures.

    We might later convert pneigh to RCU and revert this patch.

    sysbot reported :

    BUG: KASAN: use-after-free in pneigh_get_next.isra.0+0x24b/0x280 net/core/neighbour.c:3158
    Read of size 8 at addr ffff888097f2a700 by task syz-executor.0/9825

    CPU: 1 PID: 9825 Comm: syz-executor.0 Not tainted 5.2.0-rc4+ #32
    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+0x172/0x1f0 lib/dump_stack.c:113
    print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
    __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
    kasan_report+0x12/0x20 mm/kasan/common.c:614
    __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
    pneigh_get_next.isra.0+0x24b/0x280 net/core/neighbour.c:3158
    neigh_seq_next+0xdb/0x210 net/core/neighbour.c:3240
    seq_read+0x9cf/0x1110 fs/seq_file.c:258
    proc_reg_read+0x1fc/0x2c0 fs/proc/inode.c:221
    do_loop_readv_writev fs/read_write.c:714 [inline]
    do_loop_readv_writev fs/read_write.c:701 [inline]
    do_iter_read+0x4a4/0x660 fs/read_write.c:935
    vfs_readv+0xf0/0x160 fs/read_write.c:997
    kernel_readv fs/splice.c:359 [inline]
    default_file_splice_read+0x475/0x890 fs/splice.c:414
    do_splice_to+0x127/0x180 fs/splice.c:877
    splice_direct_to_actor+0x2d2/0x970 fs/splice.c:954
    do_splice_direct+0x1da/0x2a0 fs/splice.c:1063
    do_sendfile+0x597/0xd00 fs/read_write.c:1464
    __do_sys_sendfile64 fs/read_write.c:1525 [inline]
    __se_sys_sendfile64 fs/read_write.c:1511 [inline]
    __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1511
    do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
    entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x4592c9
    Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
    RSP: 002b:00007f4aab51dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
    RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00000000004592c9
    RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000005
    RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000080000000 R11: 0000000000000246 R12: 00007f4aab51e6d4
    R13: 00000000004c689d R14: 00000000004db828 R15: 00000000ffffffff

    Allocated by task 9827:
    save_stack+0x23/0x90 mm/kasan/common.c:71
    set_track mm/kasan/common.c:79 [inline]
    __kasan_kmalloc mm/kasan/common.c:489 [inline]
    __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
    kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
    __do_kmalloc mm/slab.c:3660 [inline]
    __kmalloc+0x15c/0x740 mm/slab.c:3669
    kmalloc include/linux/slab.h:552 [inline]
    pneigh_lookup+0x19c/0x4a0 net/core/neighbour.c:731
    arp_req_set_public net/ipv4/arp.c:1010 [inline]
    arp_req_set+0x613/0x720 net/ipv4/arp.c:1026
    arp_ioctl+0x652/0x7f0 net/ipv4/arp.c:1226
    inet_ioctl+0x2a0/0x340 net/ipv4/af_inet.c:926
    sock_do_ioctl+0xd8/0x2f0 net/socket.c:1043
    sock_ioctl+0x3ed/0x780 net/socket.c:1194
    vfs_ioctl fs/ioctl.c:46 [inline]
    file_ioctl fs/ioctl.c:509 [inline]
    do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
    ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
    __do_sys_ioctl fs/ioctl.c:720 [inline]
    __se_sys_ioctl fs/ioctl.c:718 [inline]
    __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
    do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
    entry_SYSCALL_64_after_hwframe+0x49/0xbe

    Freed by task 9824:
    save_stack+0x23/0x90 mm/kasan/common.c:71
    set_track mm/kasan/common.c:79 [inline]
    __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
    kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
    __cache_free mm/slab.c:3432 [inline]
    kfree+0xcf/0x220 mm/slab.c:3755
    pneigh_ifdown_and_unlock net/core/neighbour.c:812 [inline]
    __neigh_ifdown+0x236/0x2f0 net/core/neighbour.c:356
    neigh_ifdown+0x20/0x30 net/core/neighbour.c:372
    arp_ifdown+0x1d/0x21 net/ipv4/arp.c:1274
    inetdev_destroy net/ipv4/devinet.c:319 [inline]
    inetdev_event+0xa14/0x11f0 net/ipv4/devinet.c:1544
    notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
    __raw_notifier_call_chain kernel/notifier.c:396 [inline]
    raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
    call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1749
    call_netdevice_notifiers_extack net/core/dev.c:1761 [inline]
    call_netdevice_notifiers net/core/dev.c:1775 [inline]
    rollback_registered_many+0x9b9/0xfc0 net/core/dev.c:8178
    rollback_registered+0x109/0x1d0 net/core/dev.c:8220
    unregister_netdevice_queue net/core/dev.c:9267 [inline]
    unregister_netdevice_queue+0x1ee/0x2c0 net/core/dev.c:9260
    unregister_netdevice include/linux/netdevice.h:2631 [inline]
    __tun_detach+0xd8a/0x1040 drivers/net/tun.c:724
    tun_detach drivers/net/tun.c:741 [inline]
    tun_chr_close+0xe0/0x180 drivers/net/tun.c:3451
    __fput+0x2ff/0x890 fs/file_table.c:280
    ____fput+0x16/0x20 fs/file_table.c:313
    task_work_run+0x145/0x1c0 kernel/task_work.c:113
    tracehook_notify_resume include/linux/tracehook.h:185 [inline]
    exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
    prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
    syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
    do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
    entry_SYSCALL_64_after_hwframe+0x49/0xbe

    The buggy address belongs to the object at ffff888097f2a700
    which belongs to the cache kmalloc-64 of size 64
    The buggy address is located 0 bytes inside of
    64-byte region [ffff888097f2a700, ffff888097f2a740)
    The buggy address belongs to the page:
    page:ffffea00025fca80 refcount:1 mapcount:0 mapping:ffff8880aa400340 index:0x0
    flags: 0x1fffc0000000200(slab)
    raw: 01fffc0000000200 ffffea000250d548 ffffea00025726c8 ffff8880aa400340
    raw: 0000000000000000 ffff888097f2a000 0000000100000020 0000000000000000
    page dumped because: kasan: bad access detected

    Memory state around the buggy address:
    ffff888097f2a600: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
    ffff888097f2a680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
    >ffff888097f2a700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
    ^
    ffff888097f2a780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
    ffff888097f2a800: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc

    Fixes: 767e97e1e0db ("neigh: RCU conversion of struct neighbour")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/core/neighbour.c | 7 +++++++
    1 file changed, 7 insertions(+)

    --- a/net/core/neighbour.c
    +++ b/net/core/neighbour.c
    @@ -2743,6 +2743,7 @@ static void *neigh_get_idx_any(struct se
    }

    void *neigh_seq_start(struct seq_file *seq, loff_t *pos, struct neigh_table *tbl, unsigned int neigh_seq_flags)
    + __acquires(tbl->lock)
    __acquires(rcu_bh)
    {
    struct neigh_seq_state *state = seq->private;
    @@ -2753,6 +2754,7 @@ void *neigh_seq_start(struct seq_file *s

    rcu_read_lock_bh();
    state->nht = rcu_dereference_bh(tbl->nht);
    + read_lock(&tbl->lock);

    return *pos ? neigh_get_idx_any(seq, pos) : SEQ_START_TOKEN;
    }
    @@ -2786,8 +2788,13 @@ out:
    EXPORT_SYMBOL(neigh_seq_next);

    void neigh_seq_stop(struct seq_file *seq, void *v)
    + __releases(tbl->lock)
    __releases(rcu_bh)
    {
    + struct neigh_seq_state *state = seq->private;
    + struct neigh_table *tbl = state->tbl;
    +
    + read_unlock(&tbl->lock);
    rcu_read_unlock_bh();
    }
    EXPORT_SYMBOL(neigh_seq_stop);

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