"I've just released Linux 2.4.36-pre1," announced 2.4 maintainer Willy Tarreau. He described a new feature found in the first pre-release:
"In private discussions, Solar Designer proposed to restrict the ability to map the NULL address to CAP_RAW_IO capable processes only. The idea behind this was to prevent 'normal' users from trying to exploit NULL dereferences in the kernel which have not been discovered yet. This is purely a preventive measure."
Willy added that a similar feature exists in the 2.6 kernel, "Chris Wright noted that 2.6 already has a somewhat similar feature brought by Eric Paris, which introduces a sysctl by which the admin can set the lower mappable address." He also noted that the feature can be disabled, "Alan Cox indicated that it was desirable to be able to dynamically disable the feature because some (very) rare programs map the NULL pointer to speed up their walk through linked lists by avoiding NULL pointer checks." Finally he asked for testers, "please report any breakage you would detect when enabling it. We're pretty confident that almost every applications will not see any difference since no normal application maps NULL. But it would be interesting to identify the "special" ones."
Linus recently returned from a two week vacation, announcing the release of "a largish 2.5.8-pre1 patch". Following the announcement, he commented on the earlier April Fool's message. He says, "PS.