BUG: please report to dccp@vger.kernel.org => prev = 0, last = 0 at net/dccp/ccids/lib/packet_history.c:LINE/tfrc_rx_his

[syzbot]

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+998587...@syzkaller.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 dc...@vger.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


---
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[Eric Biggers]

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...@vger.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

[Dmitry Vyukov]

I think this happened when we started truncating kernel crash titles
to 120 columns, so it's intentional.
However, the dup command did not pass. It's hard to understand who
received what today, but this suggests that somebody altered email in
the command to dc...@vger.kernel.org:
https://groups.google.com/forum/message/raw?msg=syzkaller-bugs/GMndq4-h7BI/VIz4aBEOAwAJ
We can also mark the old one as invalid.

[Eric Biggers]

Ah, that was my fault -- I must have copied the bug title from the
syzkaller-bugs Google Groups page, which had mangled the email address in the
bug title. The actual title was: