linux-kernel - [PATCH -v3 2/3] SELinux: call cap_file_mmap in selinux_file

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Message-ID: <20090729185627.21757.92301.stgit@paris.rdu.redhat.com>
Date:	Wed, 29 Jul 2009 14:56:27 -0400
From:	Eric Paris <eparis@...hat.com>
To:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov
Cc:	jwcart2@...ho.nsa.gov, eparis@...hat.com, sds@...ho.nsa.gov,
	spender@...ecurity.net, dwalsh@...hat.com, cl@...ux-foundation.org,
	arjan@...radead.org, alan@...rguk.ukuu.org.uk, kees@...flux.net,
	csellers@...sys.com, penguin-kernel@...ove.sakura.ne.jp
Subject: [PATCH -v3 2/3] SELinux: call cap_file_mmap in selinux_file_mmap

Currently SELinux does not check CAP_SYS_RAWIO in the file_mmap hook.  This
means there is no DAC check on the ability to mmap low addresses in the
memory space.  This function adds the DAC check for CAP_SYS_RAWIO while
maintaining the selinux check on mmap_zero.  This means that processes
which need to mmap low memory will need CAP_SYS_RAWIO and mmap_zero but will
NOT need the SELinux sys_rawio capability.

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

 security/selinux/hooks.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e65677d..8a78f58 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3034,9 +3034,21 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
 	int rc = 0;
 	u32 sid = current_sid();
 
-	if (addr < mmap_min_addr)
+	/*
+	 * notice that we are intentionally putting the SELinux check before
+	 * the secondary cap_file_mmap check.  This is such a likely attempt
+	 * at bad behaviour/exploit that we always want to get the AVC, even
+	 * if DAC would have also denied the operation.
+	 */
+	if (addr < mmap_min_addr) {
 		rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
 				  MEMPROTECT__MMAP_ZERO, NULL);
+		if (rc)
+			return rc;
+	}
+
+	/* do DAC check on address space usage */
+	rc = cap_file_mmap(file, reqprot, prot, flags, addr, addr_only);
 	if (rc || addr_only)
 		return rc;
 

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