New subject: [Bug 55487] winpcap: pcap_dispatch doesn't work with count argument -1

26 Aug 2023


      https://bugs.winehq.org/show_bug.cgi?id=55487
Bug ID: 55487
           Summary: winpcap: pcap_dispatch doesn't work with count
                    argument -1
           Product: Wine
           Version: 8.14
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: wpcap
          Assignee: wine-bugs@winehq.org
          Reporter: amubtdx@gmail.com
      Distribution: ---
Hi,
While trying to use a Windows program that uses WinPcap, it is not receiving
anything from `pcap_dispatch`.
`pcap_dispatch` is a function to receive raw packets from the ethernet adapter.
In the Windows program, `pcap_dispatch` is called with the `cnt` argument `-1`.
According to WinPcap documentation of `pcap_dispatch`
(https://www.winpcap.org/docs/docs_41b5/html/group__wpcapfunc.html#g60ce104cd...):
...
A cnt of -1 processes all the packets received in one buffer when reading a
live capture, or all the packets in the file when reading a ``savefile''
But Wine implementation of `pcap_dispatch` does this:
```c
int CDECL pcap_dispatch( struct pcap *pcap, int count,
                         void (CALLBACK *callback)(unsigned char *, const
struct pcap_pkthdr_win32 *, const unsigned char *),
                         unsigned char *user )
{
    int processed = 0;
TRACE( "%p, %d, %p, %p\n", pcap, count, callback, user );
while (processed < count)
    {
```
See here:
https://github.com/wine-mirror/wine/blob/bd10252332491bc39100f230540b14d59f0...
When `count` is `-1`, `while (processed < count)` exit immediately without
processing any packets.
I've tried a local build using this condition instead, and it fixes the issue:
`while (count <= 0 || processed < count)`.
I use `count <= 0` to match libpcap's way of checking unlimited count.
```c
// pcap-int.h:
#define PACKET_COUNT_IS_UNLIMITED(count)    ((count) <= 0)
// pcap-netfilter-linux.c, end of function netfilter_read_linux:
// [...]
if (count >= max_packets && !PACKET_COUNT_IS_UNLIMITED(max_packets)) {
// [...]
```
Note: here, `count` is the number of processed packets so far and `max_packet`
is the value of `cnt`/`count` given to `pcap_dispatch`.
See here:
https://github.com/the-tcpdump-group/libpcap/blob/bf8bfc74b2c8e893b2af2d657a...
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[Bug 55487] New: winpcap: pcap_dispatch doesn't work with count argument -1