linux-kernel - [PATCH 3/3] security: allow capable check to permit mmap or low vm space

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Date:	Fri, 16 Nov 2007 15:55:45 -0500
From:	Eric Paris <eparis@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	jmorris@...ei.org, sds@...ho.nsa.gov, selinux@...ho.nsa.gov,
	alan@...hat.com, chrisw@...hat.com, hpa@...or.com,
	akpm@...ux-foundation.org
Subject: [PATCH 3/3] 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.

Signed-off-by: Eric Paris <eparis@...hat.com>

---

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

diff --git a/security/dummy.c b/security/dummy.c
index 6d895ad..3ccfbbe 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -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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