IsBad*Ptr patch

Christopher Faylor
Wed Aug 7 14:04:00 GMT 2002

On Wed, Aug 07, 2002 at 09:50:06PM +0100, Conrad Scott wrote:
>There's nothing explicitly in there (or SUSv3, which is what I'm
>using) but the page only mentions *using* it if the address
>argument is not null.  Also, the code examples in Stevens's "Unix
>Network Programming" for recvmsg(2) simply set the address pointer
>to null and leave the length pointer uninitialised, which would
>make cygwin barf if it were also to check the address length

I don't have this reference.  How can a pointer be uninitialized?

Do they do something like

int *len;
recvmsg(..., NULL, len);


That sounds like bad programming to me, but if that is the standard
then ok.

>> >@@ -970,7 +978,7 @@
>> > extern "C" struct hostent *
>> > cygwin_gethostbyaddr (const char *addr, int len, int type)
>> > {
>> >-  if (__check_null_invalid_struct_errno (addr, len))
>> >+  if (__check_invalid_read_ptr_errno (addr, len))
>> >     return NULL;
>> Isn't addr writable?  invalid_struct_errno checks that addr is
>in writable
>> memory.
>It can't be writable: it's a const char *, and this is exactly one
>of cases I found by changing the signature of the checking
>functions.  The addr is just a key into the hosts database.

Doh! Answering technical email with a splitting headache during
meetings.  Always a sure way to embarrass myself.

>I hope my sprinkled replies have helped sort things out: I've
>spent a while going through the SUSv3 definitions checking these.
>Most of it falls out from the const / non-const state of the
>arguments though.

Yep.  Sorry for the noise.

I'm not 100% convinced about the len arguments but go ahead and check
this in and we can sort that out later.  I doubt that anyone would ever
complain about your changes ("Wah!  I wanted to get a ENOSYS by passing
a bad length argument and you wouldn't let me!") so this is really a

Hopefully Corinna won't mind since this is technically her code but 
I think you've more than adequately explained things.


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