linux-kernel - [PATCH 1/2] VM/SELinux: require CAP_SYS_RAWIO for all mmap

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Date:	Tue, 21 Jul 2009 10:41:58 -0400
From:	Eric Paris <eparis@...hat.com>
To:	linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org
Cc:	sds@...ho.nsa.gov, jmorris@...ei.org, spender@...ecurity.net,
	dwalsh@...hat.com, cl@...ux-foundation.org, arjan@...radead.org,
	alan@...rguk.ukuu.org.uk, kyle@...artin.ca, cpardy@...hat.com,
	arnd@...db.de
Subject: [PATCH 1/2] VM/SELinux: require CAP_SYS_RAWIO for all mmap_zero
	operations

Currently non-SELinux systems need CAP_SYS_RAWIO for an application to mmap
the 0 page.  On SELinux systems they need a specific SELinux permission,
but do not need CAP_SYS_RAWIO.  This has proved to be a poor decision by
the SELinux team as, by default, SELinux users are logged in unconfined and
thus a malicious non-root has nothing stopping them from mapping the 0 page
of virtual memory.

On a non-SELinux system, a malicious non-root user is unable to do this, as
they need CAP_SYS_RAWIO.

This patch checks CAP_SYS_RAWIO for all operations which attemt to map a
page below mmap_min_addr.

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

 include/linux/security.h |    2 --
 mm/mmap.c                |   10 ++++++++++
 mm/mremap.c              |    8 ++++++++
 mm/nommu.c               |    3 +++
 security/capability.c    |    2 --
 5 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 1459091..f7d198a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -2197,8 +2197,6 @@ static inline int security_file_mmap(struct file *file, unsigned long reqprot,
 				     unsigned long addr,
 				     unsigned long addr_only)
 {
-	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
-		return -EACCES;
 	return 0;
 }
 
diff --git a/mm/mmap.c b/mm/mmap.c
index 34579b2..37fdc90 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1047,6 +1047,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 		}
 	}
 
+	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+		return -EACCES;
+
 	error = security_file_mmap(file, reqprot, prot, flags, addr, 0);
 	if (error)
 		return error;
@@ -1657,6 +1660,10 @@ static int expand_downwards(struct vm_area_struct *vma,
 		return -ENOMEM;
 
 	address &= PAGE_MASK;
+
+	if ((address < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+		return -EACCES;
+
 	error = security_file_mmap(NULL, 0, 0, 0, address, 1);
 	if (error)
 		return error;
@@ -1998,6 +2005,9 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
 	if (is_hugepage_only_range(mm, addr, len))
 		return -EINVAL;
 
+	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+		return -EACCES;
+
 	error = security_file_mmap(NULL, 0, 0, 0, addr, 1);
 	if (error)
 		return error;
diff --git a/mm/mremap.c b/mm/mremap.c
index a39b7b9..066e73d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -299,6 +299,10 @@ unsigned long do_mremap(unsigned long addr,
 		if ((addr <= new_addr) && (addr+old_len) > new_addr)
 			goto out;
 
+		ret = -EACCES;
+		if ((new_addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+			goto out;
+
 		ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
 		if (ret)
 			goto out;
@@ -407,6 +411,10 @@ unsigned long do_mremap(unsigned long addr,
 				goto out;
 			}
 
+			ret = -EACCES;
+			if ((new_addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+				goto out;
+
 			ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
 			if (ret)
 				goto out;
diff --git a/mm/nommu.c b/mm/nommu.c
index 53cab10..c1f3eff 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -995,6 +995,9 @@ static int validate_mmap_request(struct file *file,
 	}
 
 	/* allow the security API to have its say */
+	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+		return -EACCES;
+
 	ret = security_file_mmap(file, reqprot, prot, flags, addr, 0);
 	if (ret < 0)
 		return ret;
diff --git a/security/capability.c b/security/capability.c
index f218dd3..a3a5d9b 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -334,8 +334,6 @@ static int cap_file_mmap(struct file *file, unsigned long reqprot,
 			 unsigned long prot, unsigned long flags,
 			 unsigned long addr, unsigned long addr_only)
 {
-	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
-		return -EACCES;
 	return 0;
 }
 

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