mmap_min_addr and security modules [LWN.net]

mmap_min_addr and security modules

Posted Jul 20, 2009 21:53 UTC (Mon) by corbet (editor, #1)
In reply to: mmap_min_addr and security modules by fjpop
Parent article: Fun with NULL pointers, part 1

The code which performs the check was:

static inline unsigned long round_hint_to_min(unsigned long hint)
{
#ifdef CONFIG_SECURITY
	hint &= PAGE_MASK;
	if (((void *)hint != NULL) &&
	    (hint < mmap_min_addr))
		return PAGE_ALIGN(mmap_min_addr);
#endif
	return hint;
}

So it was taken out at compile time; the presence of an actual security module is not really relevant.

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mmap_min_addr and security modules

Posted Jul 20, 2009 22:15 UTC (Mon) by spender (subscriber, #23067) [Link]

That's not the right check. security_file_mmap (which is either set by the capabilities module or overriden by the SELinux module) is what implements the final check. The one you pasted doesn't even apply for MAP_FIXED but is just to ensure that the allocator doesn't choose an address below mmap_min_addr when only a hint is specified.

If SELinux is compiled into the kernel, it needs to be disabled at boot via the kernel command-line, otherwise it registers its hooks with LSM and overrides that of the capabilities module for security_file_mmap which performs the mmap_min_addr check.

-Brad