security: allow capable check to permit mmap or low vm space

On a kernel with CONFIG_SECURITY but without an LSM which implements security_file_mmap it is impossible for an application to mmap addresses lower than mmap_min_addr. Based on a suggestion from a developer in the openwall community this patch adds a check for CAP_SYS_RAWIO. It is assumed that any process with this capability can harm the system a lot more easily than writing some stuff on the zero page and then trying to get the kernel to trip over itself. It also means that programs like X on i686 which use vm86 emulation can work even with mmap_min_addr set.

---

 security/dummy.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 6d895ad..3ccfbbe 100644
@@ -426,7 +426,7 @@ static int dummy_file_mmap (struct file *file, unsigned long reqprot,
 			    unsigned long addr,
 			    unsigned long addr_only)
 {
-	if (addr < mmap_min_addr)
+	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
 		return -EACCES;
 	return 0;
 }

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Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/selinux-2.6.git#for-akpm

If nobody hollers, I'll push it to Linus when the next merge window opens.

- James

James Morris
<[email protected]>

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