No it wouldn't. They clearly included the ability to return null to allow for when the data exceeds the capacity of the system. There is no provision for returning a pointer to memory that cannot be used.

You might think, but that's not how how conformance (of an ISO C implementation to the standard) works.

For an implementation to be deemed conforming, it just has to be demonstrated to successfully translate and execute one program that tests each of the minimum implementation limits.

See 5.2.4.1 in http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf

Only if no such program can be found can we then conclude that the implementation is nonconforming (and if the reason for not finding such a program is this overcommit issue, then we can blame that issue).

Your Linux system is indeed nonconforming if it is so low on memory that, for instance, no C program can allocate a 65535 byte object (that can be actually initialized, and used: a real object). Basically the memory situation has to be so severe that it takes the implementation below the minimum limits, whereby we can clearly demonstrate nonconformance.