[PATCH] Cygwin: add fd validation to mq_* functions

[mark@maxrnd.com]

I believe a positive but nonexistent fd passed to cygheap_getfd results in a -1, so that case should be covered by this patch.
However I botched the coding for mq_close. That fix plus anything else needed per reviews will appear as a v2.
Thanks & Regards,
..mark

Jan 15, 2025 3:35:43 AM Christian Franke <Christian.Franke@t-online.de>:

> Mark Geisert wrote:
>> Validate the fd returned by cygheap_getfd operating on given mqd.
>> 
>> Reported-by: Christian Franke <Christian.Franke@t-online.de>
>> Addresses: https://cygwin.com/pipermail/cygwin/2025-January/257090.html
>> Signed-off-by: Mark Geisert <mark@maxrnd.com>
>> Fixes: 46f3b0ce85a9 (Cygwin: POSIX msg queues: move all mq_* functionality into fhandler_mqueue)
>> 
>> ---
>>   winsup/cygwin/posix_ipc.cc | 88 +++++++++++++++++++++++---------------
>>   1 file changed, 53 insertions(+), 35 deletions(-)
>> 
>> diff --git a/winsup/cygwin/posix_ipc.cc b/winsup/cygwin/posix_ipc.cc
>> index 34fd2ba34..3ce1ecda6 100644
>> --- a/winsup/cygwin/posix_ipc.cc
>> +++ b/winsup/cygwin/posix_ipc.cc
>> @@ -225,11 +225,14 @@ mq_getattr (mqd_t mqd, struct mq_attr *mqstat)
>>     int ret = -1;
>>       cygheap_fdget fd ((int) mqd, true);
>> -  fhandler_mqueue *fh = fd->is_mqueue ();
>> -  if (!fh)
>> -    set_errno (EBADF);
>> -  else
>> -    ret = fh->mq_getattr (mqstat);
>> +  if (fd >= 0)
>> +    {
>> +      fhandler_mqueue *fh = fd->is_mqueue ();
>> +      if (!fh)
>> +        set_errno (EBADF);
>> +      else
>> +        ret = fh->mq_getattr (mqstat);
>> +    }
> 
> Sorry, I forgot to mention that the testcase also "works" (segfaults) if a positive but nonexistent fd is used. I'm not sure whether the (fd >= 0) check is sufficient.