selinux: export initial SID contexts via selinuxfs

Make the initial SID contexts accessible to userspace via selinuxfs.
An initial use of this support will be to make the unlabeled context
available to libselinux for use for invalidated userspace SIDs.

Signed-off-by: James Carter <jwcart2@tycho.nsa.gov>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 93b3177c7585..e24235c59ddf 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -102,6 +102,9 @@ enum sel_inos {
         SEL_COMPAT_NET, /* whether to use old compat network packet controls */
 };
 
+#define SEL_INITCON_INO_OFFSET  0x01000000
+#define SEL_INO_MASK            0x00ffffff
+
 #define TMPBUFLEN       12
 static ssize_t sel_read_enforce(struct file *filp, char __user *buf,
                                 size_t count, loff_t *ppos)
@@ -1240,6 +1243,55 @@ out:
         return ret;
 }
 
+static ssize_t sel_read_initcon(struct file * file, char __user *buf,
+                                size_t count, loff_t *ppos)
+{
+        struct inode *inode;
+        char *con;
+        u32 sid, len;
+        ssize_t ret;
+
+        inode = file->f_path.dentry->d_inode;
+        sid = inode->i_ino&SEL_INO_MASK;
+        ret = security_sid_to_context(sid, &con, &len);
+        if (ret < 0)
+                return ret;
+
+        ret = simple_read_from_buffer(buf, count, ppos, con, len);
+        kfree(con);
+        return ret;
+}
+
+static const struct file_operations sel_initcon_ops = {
+        .read           = sel_read_initcon,
+};
+
+static int sel_make_initcon_files(struct dentry *dir)
+{
+        int i, ret = 0;
+
+        for (i = 1; i <= SECINITSID_NUM; i++) {
+                struct inode *inode;
+                struct dentry *dentry;
+                dentry = d_alloc_name(dir, security_get_initial_sid_context(i));
+                if (!dentry) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
+
+                inode = sel_make_inode(dir->d_sb, S_IFREG|S_IRUGO);
+                if (!inode) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
+                inode->i_fop = &sel_initcon_ops;
+                inode->i_ino = i|SEL_INITCON_INO_OFFSET;
+                d_add(dentry, inode);
+        }
+out:
+        return ret;
+}
+
 static int sel_make_dir(struct inode *dir, struct dentry *dentry)
 {
         int ret = 0;
@@ -1336,6 +1388,21 @@ static int sel_fill_super(struct super_block * sb, void * data, int silent)
         ret = sel_make_avc_files(dentry);
         if (ret)
                 goto err;
+
+        dentry = d_alloc_name(sb->s_root, "initial_contexts");
+        if (!dentry) {
+                ret = -ENOMEM;
+                goto err;
+        }
+
+        ret = sel_make_dir(root_inode, dentry);
+        if (ret)
+                goto err;
+
+        ret = sel_make_initcon_files(dentry);
+        if (ret)
+                goto err;
+
 out:
         return ret;
 err: