Message-ID: <20180509050509.GE711@sol.localdomain>
Date:   Tue, 8 May 2018 22:05:09 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     dccp@...r.kernel.org, Gerrit Renker <gerrit@....abdn.ac.uk>
Cc:     syzbot <syzbot+99858724c0ba555a12ea@...kaller.appspotmail.com>,
        davem@...emloft.net, garsilva@...eddedor.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: BUG: please report to dccp@...r.kernel.org => prev = 0, last = 0
 at net/dccp/ccids/lib/packet_history.c:LINE/tfrc_rx_his

On Sat, May 05, 2018 at 05:57:02PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    c1c07416cdd4 Merge tag 'kbuild-fixes-v4.17' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d5de47800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5a1dc06635c10d27
> dashboard link: https://syzkaller.appspot.com/bug?extid=99858724c0ba555a12ea
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=170afde7800000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141b4be7800000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+99858724c0ba555a12ea@...kaller.appspotmail.com
> 
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> BUG: please report to dccp@...r.kernel.org => prev = 0, last = 0 at
> net/dccp/ccids/lib/packet_history.c:425/tfrc_rx_hist_sample_rtt()
> CPU: 0 PID: 4495 Comm: syz-executor551 Not tainted 4.17.0-rc3+ #34
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>  tfrc_rx_hist_sample_rtt.cold.3+0x54/0x5c
> net/dccp/ccids/lib/packet_history.c:422
>  ccid3_hc_rx_packet_recv+0x5c8/0xed0 net/dccp/ccids/ccid3.c:765
>  ccid_hc_rx_packet_recv net/dccp/ccid.h:185 [inline]
>  dccp_deliver_input_to_ccids+0xf0/0x280 net/dccp/input.c:180
>  dccp_rcv_established+0x87/0xb0 net/dccp/input.c:378
>  dccp_v4_do_rcv+0x153/0x180 net/dccp/ipv4.c:654
>  sk_backlog_rcv include/net/sock.h:909 [inline]
>  __sk_receive_skb+0x3a2/0xd60 net/core/sock.c:513
>  dccp_v4_rcv+0x10e5/0x1f3f net/dccp/ipv4.c:875
>  ip_local_deliver_finish+0x2e3/0xd80 net/ipv4/ip_input.c:215
>  NF_HOOK include/linux/netfilter.h:288 [inline]
>  ip_local_deliver+0x1e1/0x720 net/ipv4/ip_input.c:256
>  dst_input include/net/dst.h:450 [inline]
>  ip_rcv_finish+0x81b/0x2200 net/ipv4/ip_input.c:396
>  NF_HOOK include/linux/netfilter.h:288 [inline]
>  ip_rcv+0xb70/0x143d net/ipv4/ip_input.c:492
>  __netif_receive_skb_core+0x26f5/0x3630 net/core/dev.c:4592
>  __netif_receive_skb+0x2c/0x1e0 net/core/dev.c:4657
>  process_backlog+0x219/0x760 net/core/dev.c:5337
>  napi_poll net/core/dev.c:5735 [inline]
>  net_rx_action+0x7b7/0x1930 net/core/dev.c:5801
>  __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285
>  do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1046
>  </IRQ>
>  do_softirq.part.17+0x14d/0x190 kernel/softirq.c:329
>  do_softirq arch/x86/include/asm/preempt.h:23 [inline]
>  __local_bh_enable_ip+0x1ec/0x230 kernel/softirq.c:182
>  local_bh_enable include/linux/bottom_half.h:32 [inline]
>  rcu_read_unlock_bh include/linux/rcupdate.h:728 [inline]
>  ip_finish_output2+0xab2/0x1840 net/ipv4/ip_output.c:231
>  ip_finish_output+0x828/0xf80 net/ipv4/ip_output.c:317
>  NF_HOOK_COND include/linux/netfilter.h:277 [inline]
>  ip_output+0x21b/0x850 net/ipv4/ip_output.c:405
>  dst_output include/net/dst.h:444 [inline]
>  ip_local_out+0xc5/0x1b0 net/ipv4/ip_output.c:124
>  ip_queue_xmit+0x9d7/0x1f70 net/ipv4/ip_output.c:504
>  dccp_transmit_skb+0x999/0x12e0 net/dccp/output.c:142
>  dccp_xmit_packet+0x250/0x790 net/dccp/output.c:281
>  dccp_write_xmit+0x190/0x1f0 net/dccp/output.c:363
>  dccp_sendmsg+0x8c7/0x1020 net/dccp/proto.c:818
>  inet_sendmsg+0x19f/0x690 net/ipv4/af_inet.c:798
>  sock_sendmsg_nosec net/socket.c:629 [inline]
>  sock_sendmsg+0xd5/0x120 net/socket.c:639
>  ___sys_sendmsg+0x525/0x940 net/socket.c:2117
>  __sys_sendmmsg+0x240/0x6f0 net/socket.c:2212
>  __do_sys_sendmmsg net/socket.c:2241 [inline]
>  __se_sys_sendmmsg net/socket.c:2238 [inline]
>  __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2238
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x445d09
> RSP: 002b:00007f3c7eff5d88 EFLAGS: 00000293 ORIG_RAX: 0000000000000133
> RAX: ffffffffffffffda RBX: 00000000006dac40 RCX: 0000000000445d09
> RDX: 0000000000000001 RSI: 000000
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
> merged
> into any tree, please reply to this email with:
> #syz fix: exact-commit-title
> If you want to test a patch for this bug, please reply with:
> #syz test: git://repo/address.git branch
> and provide the patch inline or as an attachment.
> To mark this as a duplicate of another syzbot report, please reply with:
> #syz dup: exact-subject-of-another-report

There's already a bug report with this title, this one just had a few characters
truncated from the end.  Dmitry, is that intentional?  The other one is
https://groups.google.com/forum/#!msg/syzkaller-bugs/u5nq3PdPkIc/bBFjKHXPAgAJ:

#syz dup: BUG: please report to dc...@...r.kernel.org => prev = 0, last = 0 at net/dccp/ccids/lib/packet_history.c:LINE/tfrc_rx_hist_sample_rtt()

Anyway, this is apparently a DCCP bug, and as I posted on the other thread it's
easily reproducible with the following program.  Gerrit, are you still the DCCP
maintainer, or is the MAINTAINERS file outdated?

	#include <linux/dccp.h>
	#include <linux/in.h>
	#include <sys/socket.h>
	#include <sys/wait.h>
	#include <unistd.h>

	int main()
	{
		struct sockaddr_in addr = { .sin_family = AF_INET };
		socklen_t addrlen = sizeof(addr);
		int fd;

		while (fork())
			wait(NULL);
		fd = socket(AF_INET, SOCK_DCCP, 0);
		bind(fd, (void *)&addr, addrlen);
		getsockname(fd, (void *)&addr, &addrlen);
		listen(fd, 100);
		if (fork()) {
			fd = socket(AF_INET, SOCK_DCCP, 0);
			setsockopt(fd, SOL_DCCP, DCCP_SOCKOPT_CCID, "\x03", 1);
			connect(fd, (void *)&addr, sizeof(addr));
		} else {
			fd = accept(fd, NULL, 0);
		}
		for (int i = 0; i < 1000; i++)
			write(fd, "X", 1);
	}

- Eric

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