Re: Libpcap - pcapfindalldevs

[Johan Mazel <johan.mazel () gmail com>]

I wrote a short piece of code in C to show the problem.

My code is the following one:
*#include <stdio.h>
#include <pcap.h>

int main(){
    struct pcap_if * found_devices;
    int result;
    char * errbuf;
    printf("Scanning\n");
    result = pcap_findalldevs(&found_devices, errbuf);
    printf("Scan finished\n");
    if(result < 0)
    {
        printf("Device scan error %s\n",errbuf);
        return -1;
    }
    while(found_devices != NULL)
    {
        printf("%s\n",found_devices->name);
        found_devices = found_devices->next;
    }
    return 0;
}*

I compiled it with this line: gcc  -g -lpcap scan_devices.c -o scan_devices
Then, I ran it in gdb with this line: run scan_devices.
The error message is the following one:
Starting program: /.../Programmes/Tests/Scan_Interfaces/scan_devices
scan_devices
Scanning

Program received signal SIGSEGV, Segmentation fault.
0x00007fec3290afc1 in strncpy () from /lib/libc.so.6

The command bt gave me this answer:
#0  0x00007fec3290afc1 in strncpy () from /lib/libc.so.6
#1  0x00007fec32c07f1c in pcap_open_live () from /usr/lib/libpcap.so.0.8
#2  0x00007fec32c0828c in add_or_find_if () from /usr/lib/libpcap.so.0.8
#3  0x00007fec32c0853e in add_addr_to_iflist () from /usr/lib/libpcap.so.0.8
#4  0x00007fec32c06fce in pcap_findalldevs () from /usr/lib/libpcap.so.0.8
#5  0x00000000004006db in main () at scan_devices.c:9

It looks like the pcap_findalldevs function of libpcap try to open each
device (through the pcap_open_live) and thus provoke an error if the program
is not run as root.

My machine runs on Ubuntu 8.10.
My libpcap version is 0.9.8-5.

The command gcc -v gives me:
Utilisation des specs internes.
Target: x86_64-linux-gnu
Configuré avec: ../src/configure -v --with-pkgversion='Ubuntu
4.3.2-1ubuntu12' --with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Modèle de thread: posix
gcc version 4.3.2 (Ubuntu 4.3.2-1ubuntu12)

The command gdb -v gives me:
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html
>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".

If this is a bug in Libpcap, how can I submit it ?

Regards.
Johan


2009/2/2 Guy Harris <guy () alum mit edu>

> On Feb 2, 2009, at 5:39 AM, Johan Mazel wrote:
>
>  My problem is that when I'm not running the program as root, I got the
> > "Erreur de bus" in French (or "Bus Error" in english I guess) and my
> > program
> > suddenly stops.
>
> That is either a bug in your program, a bug in libpcap, or a bug in some
> other piece of software.
>
> You'd have to run your program under a debugger to see where it crashes in
> order to determine where the bug is and either
>
>        1) fix it if it's in your program
>
> or
>
>        2) report it if it's a bug in some other piece of software.
>
> -
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