[3.11.y.z extended stable] Patch "selinux: correctly label /proc inodes in use before the policy is" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    selinux: correctly label /proc inodes in use before the policy is

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 71ebe422f93a64271dff75786013b3863e00d35f Mon Sep 17 00:00:00 2001
From: Paul Moore <pmoore at redhat.com>
Date: Wed, 19 Mar 2014 16:46:18 -0400
Subject: selinux: correctly label /proc inodes in use before the policy is
 loaded

commit f64410ec665479d7b4b77b7519e814253ed0f686 upstream.

This patch is based on an earlier patch by Eric Paris, he describes
the problem below:

  "If an inode is accessed before policy load it will get placed on a
   list of inodes to be initialized after policy load.  After policy
   load we call inode_doinit() which calls inode_doinit_with_dentry()
   on all inodes accessed before policy load.  In the case of inodes
   in procfs that means we'll end up at the bottom where it does:

     /* Default to the fs superblock SID. */
     isec->sid = sbsec->sid;

     if ((sbsec->flags & SE_SBPROC) && !S_ISLNK(inode->i_mode)) {
             if (opt_dentry) {
                     isec->sclass = inode_mode_to_security_class(...)
                     rc = selinux_proc_get_sid(opt_dentry,
                                               isec->sclass,
                                               &sid);
                     if (rc)
                             goto out_unlock;
                     isec->sid = sid;
             }
     }

   Since opt_dentry is null, we'll never call selinux_proc_get_sid()
   and will leave the inode labeled with the label on the superblock.
   I believe a fix would be to mimic the behavior of xattrs.  Look
   for an alias of the inode.  If it can't be found, just leave the
   inode uninitialized (and pick it up later) if it can be found, we
   should be able to call selinux_proc_get_sid() ..."

On a system exhibiting this problem, you will notice a lot of files in
/proc with the generic "proc_t" type (at least the ones that were
accessed early in the boot), for example:

   # ls -Z /proc/sys/kernel/shmmax | awk '{ print $4 " " $5 }'
   system_u:object_r:proc_t:s0 /proc/sys/kernel/shmmax

However, with this patch in place we see the expected result:

   # ls -Z /proc/sys/kernel/shmmax | awk '{ print $4 " " $5 }'
   system_u:object_r:sysctl_kernel_t:s0 /proc/sys/kernel/shmmax

Cc: Eric Paris <eparis at redhat.com>
Signed-off-by: Paul Moore <pmoore at redhat.com>
Acked-by: Eric Paris <eparis at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 security/selinux/hooks.c | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index bf64893..021765e 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1386,15 +1386,33 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
 		isec->sid = sbsec->sid;

 		if ((sbsec->flags & SE_SBPROC) && !S_ISLNK(inode->i_mode)) {
-			if (opt_dentry) {
-				isec->sclass = inode_mode_to_security_class(inode->i_mode);
-				rc = selinux_proc_get_sid(opt_dentry,
-							  isec->sclass,
-							  &sid);
-				if (rc)
-					goto out_unlock;
-				isec->sid = sid;
-			}
+			/* We must have a dentry to determine the label on
+			 * procfs inodes */
+			if (opt_dentry)
+				/* Called from d_instantiate or
+				 * d_splice_alias. */
+				dentry = dget(opt_dentry);
+			else
+				/* Called from selinux_complete_init, try to
+				 * find a dentry. */
+				dentry = d_find_alias(inode);
+			/*
+			 * This can be hit on boot when a file is accessed
+			 * before the policy is loaded.  When we load policy we
+			 * may find inodes that have no dentry on the
+			 * sbsec->isec_head list.  No reason to complain as
+			 * these will get fixed up the next time we go through
+			 * inode_doinit() with a dentry, before these inodes
+			 * could be used again by userspace.
+			 */
+			if (!dentry)
+				goto out_unlock;
+			isec->sclass = inode_mode_to_security_class(inode->i_mode);
+			rc = selinux_proc_get_sid(dentry, isec->sclass, &sid);
+			dput(dentry);
+			if (rc)
+				goto out_unlock;
+			isec->sid = sid;
 		}
 		break;
 	}
--
1.9.1