Ping issue in 1.20+

[Denys Vlasenko]

On Thursday 27 June 2013 20:13, Giovanni Vallesi - TeeBX wrote:
> Hi All,
> after updating from busybox 1.19.4 to 1.20.2 or 1.21.0 I got a strange 
> issue using the ping applet:
> - The first icmp packet is sent and get the target reply as expected.
> - The applet continue sending icmp, but no console output.
> - Interrupting the applet report ping statistics with a large number of 
> missing packets.
> 
> After some network debugging I discovered that the every icmp packet 
> sent after the first one has a wrong checksum. Below the first two 
> captured packets in hex format.
> 
> 161	45.089741	172.31.255.109	172.31.255.1	ICMP request
> (correct checksum 0x5D76)
> 0000   00 a0 f9 2a 28 d0 00 0c 29 9b 9e 39 08 00 45 00  ...*(...)..9..E.
> 0010   00 54 00 00 40 00 40 01 e3 fa ac 1f ff 6d ac 1f  .T.. at .@......m..
> 0020   ff 01 08 00 5d 76 3e 06 00 00 46 7a 16 09 00 00  ....]v>...Fz....
> 0030   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> 0040   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> 0050   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> 0060   00 00                                            ..
> 
> 170	46.090539	172.31.255.109	172.31.255.1	ICMP request
> (wrong checksum 0xAAB9, expected 0x0830)
> 0000   00 a0 f9 2a 28 d0 00 0c 29 9b 9e 39 08 00 45 00  ...*(...)..9..E.
> 0010   00 54 00 00 40 00 40 01 e3 fa ac 1f ff 6d ac 1f  .T.. at .@......m..
> 0020   ff 01 08 00 aa b9 3e 06 00 01 8c bf 25 09 00 00  ......>.....%...
> 0030   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> 0040   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> 0050   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> 0060   00 00                                            ..

Please add debugging prints to inet_cksum() function - for one,
let's find out the value of nleft, addr[0], and the return value.
(IOW, let's find out whether we checksum over the correct buffer,
and whether we produce the same xsum we see in tcpdump.)


> Busybox was compiled using gcc 4.5 for x86 or ARM architectures, linked 
> against eglibc 2.13 or uClibc 0.9.30.1, using kernel 3.2.45 for x86 and
> 3.0.62/3.2.21 for ARMs.
> The Busybox 1.19.4 ping applet works on all the above, same issue on all 
> using 1.20.2+.
> 
> My C programming skill are really round to zero but I found that the 
> most significant code change was from this commit:
> - 
> http://git.busybox.net/busybox/commit/?id=e8f36330d9bb27f9f7e66aa6f01ff92c07d86f62
> 
> Essentially a change from a sparse/duplicated in_cksum() function 
> refactoring a common inet_cksum().

I looked at it again and it look ok.

-- 
vda