Public bug reported:
$ lsb_release -rd
Description: Ubuntu 18.04.2 LTS
Release: 18.04
$ apt-cache policy libpcap0.8
libpcap0.8:
Installiert: 1.8.1-6ubuntu1
Installationskandidat: 1.8.1-6ubuntu1
Versionstabelle:
*** 1.8.1-6ubuntu1 500
500 http://de.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
100 /var/lib/dpkg/status
I have a tool that opens the local LAN interfaces via pcap_open_live with a
timeout of 1 ms and then reads from all interfaces. The tool used to work on
Ubuntu 16.04 but hangs on Ubuntu 18.04.
When using libpcap0.8 1.7.4-2
(https://launchpad.net/ubuntu/+archive/primary/+files/libpcap0.8_1.7.4-2_amd64.deb)
the program also works on Ubuntu 18.04.
Comparing the sources at https://launchpad.net/ubuntu/+source/libpcap I saw
that a change from 1.7.4-2 to 1.8.1-6 is related to TPACKET3. Further gdb
analysis suggests that this change is the root cause (or that TPACKET3 is
broken in Ubuntu 18.04).
Please find attached a small program that you can compile and run with "g++
pcap_test.cpp -lpcap; sudo ./a.out". On a working Ubuntu/pcap when opening an
interface without traffic we see 42 times that pcap_next_ex returns 0 (timeout,
no packet available). In case of the malfunction the program waits until a
packet is available and the program either outputs no pcap_next_ex return (no
packets received) or it outputs that pcap_next_ex returns 1 (one packet read).
Attaching gdb to the hanging program show this backtrace (after "sudo apt
install libpcap0.8-dbg"):
#0 0x00007f3335fd5bc4 in __GI___poll (fds=fds@entry=0x7ffe5b2d4d50,
nfds=nfds@entry=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007f33364d09da in poll (__timeout=<optimized out>, __nfds=1,
__fds=0x7ffe5b2d4d50) at /usr/include/x86_64-linux-gnu/bits/poll2.h:46
#2 pcap_wait_for_frames_mmap (handle=handle@entry=0x55920d9d92d0) at
./pcap-linux.c:4557
#3 0x00007f33364d0c05 in pcap_read_linux_mmap_v3 (handle=0x55920d9d92d0,
max_packets=1, callback=0x7f33364cf3c0 <pcap_oneshot_mmap>, user=0x7ffe5b2d4de0
"Д\235\r\222U") at ./pcap-linux.c:5055
#4 0x00007f33364d866a in pcap_next_ex (p=<optimized out>,
pkt_header=<optimized out>, pkt_data=<optimized out>) at ./pcap.c:295
poll with timeout=-1 waits without timeout, so blocks until a packet is
read. Comments in the function for calculating the poll-timeout suggest
that this is OK and that TPACKET3 is taking care of handling the
timeout, but not having heard of TPACKET3 before I have no idea how that
could/should work.
** Affects: libpcap (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "test program"
https://bugs.launchpad.net/bugs/1825106/+attachment/5256477/+files/pcap_test.cpp
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https://bugs.launchpad.net/bugs/1825106
Title:
pcap_next_ex does not time out
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