[systemd-devel] [PATCH] libudev: fix check for too long packet

[Topi Miettinen]

On 01/23/15 03:06, Lennart Poettering wrote:
> On Sun, 18.01.15 23:57, Topi Miettinen (toiwoton at gmail.com) wrote:
> 
>> Don't use recvmsg(2) return value to check for too long packets
>> (it doesn't work) but MSG_TRUNC flag.
> 
> Why precisely doesn't this work? I mean, it will consider messages
> that are exactly as large as the buffer as too long, but otherwise the
> old check should be fine, no?

It doesn't work because the return value of recvmsg() never exceeds the
buffer size, so too large packets are never detected.

-Topi

> 
> (The new check is much nicer though, admittedly)
> 
>> ---
>>  src/libudev/libudev-monitor.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/src/libudev/libudev-monitor.c b/src/libudev/libudev-monitor.c
>> index 484fefe..d8e551b 100644
>> --- a/src/libudev/libudev-monitor.c
>> +++ b/src/libudev/libudev-monitor.c
>> @@ -609,7 +609,7 @@ retry:
>>                  return NULL;
>>          }
>>  
>> -        if (buflen < 32 || (size_t)buflen >= sizeof(buf)) {
>> +        if (buflen < 32 || smsg.msg_flags & MSG_TRUNC) {
>>                  log_debug("invalid message length");
>>                  return NULL;
>>          }
>> -- 
>> 2.1.4
>>
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> 
> 
> Lennart
>