[systemd-devel] [PATCH] libudev-monitor: ensure proper string termination

[Topi Miettinen]

On 01/25/15 03:34, Zbigniew Jędrzejewski-Szmek wrote:
> On Sat, Jan 24, 2015 at 10:39:56AM +0200, Topi Miettinen wrote:
>> Leave space for the terminating zero when reading and make sure
>> that the last byte is zero. This also makes the check for long packets
>> equivalent to code before 9c89c1ca: reject also packets with size 8192.
>> ---
>>  src/libudev/libudev-monitor.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/libudev/libudev-monitor.c b/src/libudev/libudev-monitor.c
>> index 4cfb2f6..b7fc031 100644
>> --- a/src/libudev/libudev-monitor.c
>> +++ b/src/libudev/libudev-monitor.c
>> @@ -590,7 +590,7 @@ retry:
>>          if (udev_monitor == NULL)
>>                  return NULL;
>>          iov.iov_base = &buf;
>> -        iov.iov_len = sizeof(buf);
>> +        iov.iov_len = sizeof(buf) - 1; /* Leave space for terminating zero */
>>          memzero(&smsg, sizeof(struct msghdr));
>>          smsg.msg_iov = &iov;
>>          smsg.msg_iovlen = 1;
>> @@ -642,6 +642,8 @@ retry:
>>          if (udev_device == NULL)
>>                  return NULL;
>>  
>> +        buf.raw[sizeof(buf.raw) - 1] = '\0';
>> +
>>          if (memcmp(buf.raw, "libudev", 8) == 0) {
>>                  /* udev message needs proper version magic */
>>                  if (buf.nlh.magic != htonl(UDEV_MONITOR_MAGIC)) {
> A buffer only needs to be terminated by a zero in certain cases: usually if it
> is passed to a function which expectes that. iovecs can contain binary data,
> and have an explicit size field, so they do not need to be zero-terminated.
> Is there a reason why the buffer has to be zero-terminated in this case?

String functions strcmp, strlen and strstr, used a few lines later,
expect null byte terminated strings. Alternatively they could be changed
to strncmp and friends where the scope can be limited to only the buffer.

-Topi

> 
> Zbyszek
>