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6e6fddc783
sykzaller triggered several panics similar to the below:
[...]
[ 248.851531] BUG: KASAN: use-after-free in _copy_to_user+0x5c/0x90
[ 248.857656] Read of size 985 at addr ffff8808017ffff2 by task a.out/1425
[...]
[ 248.865902] CPU: 1 PID: 1425 Comm: a.out Not tainted 4.18.0-rc4+ #13
[ 248.865903] Hardware name: Supermicro SYS-5039MS-H12TRF/X11SSE-F, BIOS 2.1a 03/08/2018
[ 248.865905] Call Trace:
[ 248.865910] dump_stack+0xd6/0x185
[ 248.865911] ? show_regs_print_info+0xb/0xb
[ 248.865913] ? printk+0x9c/0xc3
[ 248.865915] ? kmsg_dump_rewind_nolock+0xe4/0xe4
[ 248.865919] print_address_description+0x6f/0x270
[ 248.865920] kasan_report+0x25b/0x380
[ 248.865922] ? _copy_to_user+0x5c/0x90
[ 248.865924] check_memory_region+0x137/0x190
[ 248.865925] kasan_check_read+0x11/0x20
[ 248.865927] _copy_to_user+0x5c/0x90
[ 248.865930] bpf_test_finish.isra.8+0x4f/0xc0
[ 248.865932] bpf_prog_test_run_skb+0x6a0/0xba0
[...]
After scrubbing the BPF prog a bit from the noise, turns out it called
bpf_skb_change_head() for the lwt_xmit prog with headroom of 2. Nothing
wrong in that, however, this was run with repeat >> 0 in bpf_prog_test_run_skb()
and the same skb thus keeps changing until the pskb_expand_head() called
from skb_cow() keeps bailing out in atomic alloc context with -ENOMEM.
So upon return we'll basically have 0 headroom left yet blindly do the
__skb_push() of 14 bytes and keep copying data from there in bpf_test_finish()
out of bounds. Fix to check if we have enough headroom and if pskb_expand_head()
fails, bail out with error.
Another bug independent of this fix (but related in triggering above) is
that BPF_PROG_TEST_RUN should be reworked to reset the skb/xdp buffer to
it's original state from input as otherwise repeating the same test in a
loop won't work for benchmarking when underlying input buffer is getting
changed by the prog each time and reused for the next run leading to
unexpected results.
Fixes: 1cf1cae963
("bpf: introduce BPF_PROG_TEST_RUN command")
Reported-by: syzbot+709412e651e55ed96498@syzkaller.appspotmail.com
Reported-by: syzbot+54f39d6ab58f39720a55@syzkaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
191 lines
4.8 KiB
C
191 lines
4.8 KiB
C
/* Copyright (c) 2017 Facebook
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*/
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#include <linux/bpf.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/etherdevice.h>
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#include <linux/filter.h>
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#include <linux/sched/signal.h>
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static __always_inline u32 bpf_test_run_one(struct bpf_prog *prog, void *ctx)
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{
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u32 ret;
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preempt_disable();
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rcu_read_lock();
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ret = BPF_PROG_RUN(prog, ctx);
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rcu_read_unlock();
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preempt_enable();
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return ret;
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}
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static u32 bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat, u32 *time)
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{
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u64 time_start, time_spent = 0;
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u32 ret = 0, i;
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if (!repeat)
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repeat = 1;
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time_start = ktime_get_ns();
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for (i = 0; i < repeat; i++) {
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ret = bpf_test_run_one(prog, ctx);
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if (need_resched()) {
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if (signal_pending(current))
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break;
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time_spent += ktime_get_ns() - time_start;
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cond_resched();
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time_start = ktime_get_ns();
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}
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}
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time_spent += ktime_get_ns() - time_start;
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do_div(time_spent, repeat);
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*time = time_spent > U32_MAX ? U32_MAX : (u32)time_spent;
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return ret;
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}
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static int bpf_test_finish(const union bpf_attr *kattr,
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union bpf_attr __user *uattr, const void *data,
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u32 size, u32 retval, u32 duration)
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{
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void __user *data_out = u64_to_user_ptr(kattr->test.data_out);
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int err = -EFAULT;
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if (data_out && copy_to_user(data_out, data, size))
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goto out;
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if (copy_to_user(&uattr->test.data_size_out, &size, sizeof(size)))
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goto out;
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if (copy_to_user(&uattr->test.retval, &retval, sizeof(retval)))
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goto out;
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if (copy_to_user(&uattr->test.duration, &duration, sizeof(duration)))
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goto out;
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err = 0;
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out:
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return err;
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}
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static void *bpf_test_init(const union bpf_attr *kattr, u32 size,
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u32 headroom, u32 tailroom)
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{
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void __user *data_in = u64_to_user_ptr(kattr->test.data_in);
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void *data;
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if (size < ETH_HLEN || size > PAGE_SIZE - headroom - tailroom)
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return ERR_PTR(-EINVAL);
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data = kzalloc(size + headroom + tailroom, GFP_USER);
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if (!data)
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return ERR_PTR(-ENOMEM);
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if (copy_from_user(data + headroom, data_in, size)) {
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kfree(data);
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return ERR_PTR(-EFAULT);
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}
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return data;
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}
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int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
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union bpf_attr __user *uattr)
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{
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bool is_l2 = false, is_direct_pkt_access = false;
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u32 size = kattr->test.data_size_in;
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u32 repeat = kattr->test.repeat;
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u32 retval, duration;
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int hh_len = ETH_HLEN;
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struct sk_buff *skb;
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void *data;
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int ret;
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data = bpf_test_init(kattr, size, NET_SKB_PAD + NET_IP_ALIGN,
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SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
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if (IS_ERR(data))
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return PTR_ERR(data);
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switch (prog->type) {
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case BPF_PROG_TYPE_SCHED_CLS:
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case BPF_PROG_TYPE_SCHED_ACT:
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is_l2 = true;
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/* fall through */
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case BPF_PROG_TYPE_LWT_IN:
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case BPF_PROG_TYPE_LWT_OUT:
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case BPF_PROG_TYPE_LWT_XMIT:
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is_direct_pkt_access = true;
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break;
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default:
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break;
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}
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skb = build_skb(data, 0);
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if (!skb) {
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kfree(data);
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return -ENOMEM;
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}
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skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);
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__skb_put(skb, size);
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skb->protocol = eth_type_trans(skb, current->nsproxy->net_ns->loopback_dev);
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skb_reset_network_header(skb);
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if (is_l2)
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__skb_push(skb, hh_len);
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if (is_direct_pkt_access)
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bpf_compute_data_pointers(skb);
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retval = bpf_test_run(prog, skb, repeat, &duration);
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if (!is_l2) {
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if (skb_headroom(skb) < hh_len) {
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int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
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if (pskb_expand_head(skb, nhead, 0, GFP_USER)) {
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kfree_skb(skb);
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return -ENOMEM;
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}
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}
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memset(__skb_push(skb, hh_len), 0, hh_len);
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}
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size = skb->len;
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/* bpf program can never convert linear skb to non-linear */
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if (WARN_ON_ONCE(skb_is_nonlinear(skb)))
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size = skb_headlen(skb);
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ret = bpf_test_finish(kattr, uattr, skb->data, size, retval, duration);
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kfree_skb(skb);
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return ret;
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}
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int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
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union bpf_attr __user *uattr)
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{
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u32 size = kattr->test.data_size_in;
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u32 repeat = kattr->test.repeat;
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struct netdev_rx_queue *rxqueue;
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struct xdp_buff xdp = {};
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u32 retval, duration;
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void *data;
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int ret;
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data = bpf_test_init(kattr, size, XDP_PACKET_HEADROOM + NET_IP_ALIGN, 0);
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if (IS_ERR(data))
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return PTR_ERR(data);
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xdp.data_hard_start = data;
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xdp.data = data + XDP_PACKET_HEADROOM + NET_IP_ALIGN;
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xdp.data_meta = xdp.data;
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xdp.data_end = xdp.data + size;
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rxqueue = __netif_get_rx_queue(current->nsproxy->net_ns->loopback_dev, 0);
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xdp.rxq = &rxqueue->xdp_rxq;
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retval = bpf_test_run(prog, &xdp, repeat, &duration);
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if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN ||
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xdp.data_end != xdp.data + size)
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size = xdp.data_end - xdp.data;
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ret = bpf_test_finish(kattr, uattr, xdp.data, size, retval, duration);
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kfree(data);
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return ret;
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}
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