Re: [tcpdump-workers] [Patch/Workaround?] pcap-usb-linux.c

[Jean-Louis]

Jean-Louis ha scritto:

Jean-Louis ha scritto:

today I have found some bug on pcap-usb-linux.c

now i can try to tell you which are

in accordance with usbmon.txt in "mmap mode" the data is at

&mmap_area[vec[i]] + 64;

rather than

&mmap_area[vec[i]] + 48;

with mmap ther'is 16Byte filled with 0 first to the real data...

so if i.e. I have caplen = 18Byte, in file.pcap I have 16Byte with garbage (0x00) and only 2Byte with real data other 16Byte of real data is lost.

the mmap mode is *default* with kernel >= 2.6.25-rc8-mm1

I'm newbie with libpcap and I don't know how I can fix that without degrading performance

I have patched this bug, but seems to be workaround-ish

so now pcap file is ok

Index: pcap-usb-linux.c
===================================================================
RCS file: /home/jean-louis/cvsroot/libpcap/pcap-usb-linux.c,v
retrieving revision 1.5
retrieving revision 1.6
diff -c -r1.5 -r1.6
*** pcap-usb-linux.c	29 Oct 2008 19:54:46 -0000	1.5
--- pcap-usb-linux.c	30 Oct 2008 11:35:54 -0000	1.6
***************
*** 173,180 ****
  	if (len < 0) 
  		return 0;
  
! 	handle->buffer = mmap(0, len, PROT_READ, MAP_SHARED, handle->fd, 0);
! 	return handle->buffer != MAP_FAILED;
  }
  
  pcap_t *
--- 173,180 ----
  	if (len < 0) 
  		return 0;
  
! 	handle->bp = mmap(0, len, PROT_READ, MAP_SHARED, handle->fd, 0);
! 	return handle->bp != MAP_FAILED;
  }
  
  pcap_t *
***************
*** 231,248 ****
  			handle->stats_op = usb_stats_linux_bin;
  			handle->read_op = usb_read_linux_mmap;
  			handle->cleanup_op = usb_cleanup_linux_mmap;
- 
- 			/*
- 			 * "handle->fd" is a real file, so "select()" and
- 			 * "poll()" work on it.
- 			 */
- 			handle->selectable_fd = handle->fd;
- 			return 0;
  		}
! 
! 		/* can't mmap, use plain binary interface access */
! 		handle->stats_op = usb_stats_linux_bin;
! 		handle->read_op = usb_read_linux_bin;
  	}
  	else {
  		/*Binary interface not available, try open text interface */
--- 231,242 ----
  			handle->stats_op = usb_stats_linux_bin;
  			handle->read_op = usb_read_linux_mmap;
  			handle->cleanup_op = usb_cleanup_linux_mmap;
  		}
! 		else {
! 			/* can't mmap, use plain binary interface access */
! 			handle->stats_op = usb_stats_linux_bin;
! 			handle->read_op = usb_read_linux_bin;
! 		}
  	}
  	else {
  		/*Binary interface not available, try open text interface */
***************
*** 267,278 ****
--- 261,275 ----
  
  	/* for plain binary access and text access we need to allocate the read
  	 * buffer */
+ 	/* for mmap binary access we need to allocate the storing buffer for remove unneeded
+ 	 * byte filled with 0 (workaround-ish)*/
  	handle->buffer = malloc(handle->bufsize);
  	if (!handle->buffer) {
  		snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
  			 "malloc: %s", pcap_strerror(errno));
  		return PCAP_ERROR;
  	}
+ 
  	return 0;
  }
  
***************
*** 679,685 ****
  		nflush = fetch.nfetch;
  		for (i=0; i<fetch.nfetch; ++i) {
  			/* discard filler */
! 			hdr = (pcap_usb_header*) &handle->buffer[vec[i]];
  			if (hdr->event_type == '@') 
  				continue;
  
--- 676,682 ----
  		nflush = fetch.nfetch;
  		for (i=0; i<fetch.nfetch; ++i) {
  			/* discard filler */
! 			hdr = (pcap_usb_header*) &handle->bp[vec[i]];
  			if (hdr->event_type == '@') 
  				continue;
  
***************
*** 695,702 ****
  			pkth.ts.tv_sec = hdr->ts_sec;
  			pkth.ts.tv_usec = hdr->ts_usec;
  
  			handle->md.packets_read++;
! 			callback(user, &pkth, (u_char*) hdr);
  			packets++;
  		}
  
--- 692,704 ----
  			pkth.ts.tv_sec = hdr->ts_sec;
  			pkth.ts.tv_usec = hdr->ts_usec;
  
+ 			/* copy header and data in buffer 
+ 			 * for remove byte filled with 0 (workaroud-ish) */
+ 			memcpy(handle->buffer, &handle->bp[vec[i]], 48);
+ 			memcpy(handle->buffer + 48, &handle->bp[vec[i]] + 64, clen);
+ 
  			handle->md.packets_read++;
! 			callback(user, &pkth, (u_char*) handle->buffer);
  			packets++;
  		}
  
***************
*** 713,720 ****
  static void
  usb_cleanup_linux_mmap(pcap_t* handle)
  {
! 	/* buffer must not be freed because it's memory mapped */
  	/* XXX - does it need to be unmapped? */
! 	handle->buffer = NULL;
  	pcap_cleanup_live_common(handle);
  }
--- 715,726 ----
  static void
  usb_cleanup_linux_mmap(pcap_t* handle)
  {
! 	/* bp must not be freed because it's memory mapped */
  	/* XXX - does it need to be unmapped? */
! 	handle->bp = NULL;
  	pcap_cleanup_live_common(handle);
+ 
+ 	/* buffer must be freed, we have allocated this for store header and data 
+ 	 * without byte filled with 0 (workaround-ish) */
+ 	free(handle->buffer); 
  }

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