Smack: adds smackfs/ptrace interface

This allows to limit ptrace beyond the regular smack access rules.
It adds a smackfs/ptrace interface that allows smack to be configured
to require equal smack labels for PTRACE_MODE_ATTACH access.
See the changes in Documentation/security/Smack.txt below for details.

Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@partner.samsung.com>
Signed-off-by: Rafal Krypa <r.krypa@samsung.com>

security/smack/smackfs.c

@@ -53,6 +53,7 @@ enum smk_inos {
 	SMK_REVOKE_SUBJ	= 18,	/* set rules with subject label to '-' */
 	SMK_CHANGE_RULE	= 19,	/* change or add rules (long labels) */
 	SMK_SYSLOG	= 20,	/* change syslog label) */
+	SMK_PTRACE	= 21,	/* set ptrace rule */
 };
 
 /*
@@ -100,6 +101,15 @@ struct smack_known *smack_onlycap;
  */
 struct smack_known *smack_syslog_label;
 
+/*
+ * Ptrace current rule
+ * SMACK_PTRACE_DEFAULT    regular smack ptrace rules (/proc based)
+ * SMACK_PTRACE_EXACT      labels must match, but can be overriden with
+ *			   CAP_SYS_PTRACE
+ * SMACK_PTRACE_DRACONIAN  lables must match, CAP_SYS_PTRACE has no effect
+ */
+int smack_ptrace_rule = SMACK_PTRACE_DEFAULT;
+
 /*
  * Certain IP addresses may be designated as single label hosts.
  * Packets are sent there unlabeled, but only from tasks that
@@ -2243,6 +2253,68 @@ static const struct file_operations smk_syslog_ops = {
 };
 
 
+/**
+ * smk_read_ptrace - read() for /smack/ptrace
+ * @filp: file pointer, not actually used
+ * @buf: where to put the result
+ * @count: maximum to send along
+ * @ppos: where to start
+ *
+ * Returns number of bytes read or error code, as appropriate
+ */
+static ssize_t smk_read_ptrace(struct file *filp, char __user *buf,
+			       size_t count, loff_t *ppos)
+{
+	char temp[32];
+	ssize_t rc;
+
+	if (*ppos != 0)
+		return 0;
+
+	sprintf(temp, "%d\n", smack_ptrace_rule);
+	rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
+	return rc;
+}
+
+/**
+ * smk_write_ptrace - write() for /smack/ptrace
+ * @file: file pointer
+ * @buf: data from user space
+ * @count: bytes sent
+ * @ppos: where to start - must be 0
+ */
+static ssize_t smk_write_ptrace(struct file *file, const char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	char temp[32];
+	int i;
+
+	if (!smack_privileged(CAP_MAC_ADMIN))
+		return -EPERM;
+
+	if (*ppos != 0 || count >= sizeof(temp) || count == 0)
+		return -EINVAL;
+
+	if (copy_from_user(temp, buf, count) != 0)
+		return -EFAULT;
+
+	temp[count] = '\0';
+
+	if (sscanf(temp, "%d", &i) != 1)
+		return -EINVAL;
+	if (i < SMACK_PTRACE_DEFAULT || i > SMACK_PTRACE_MAX)
+		return -EINVAL;
+	smack_ptrace_rule = i;
+
+	return count;
+}
+
+static const struct file_operations smk_ptrace_ops = {
+	.write		= smk_write_ptrace,
+	.read		= smk_read_ptrace,
+	.llseek		= default_llseek,
+};
+
 /**
  * smk_fill_super - fill the smackfs superblock
  * @sb: the empty superblock
@@ -2296,6 +2368,8 @@ static int smk_fill_super(struct super_block *sb, void *data, int silent)
 			"change-rule", &smk_change_rule_ops, S_IRUGO|S_IWUSR},
 		[SMK_SYSLOG] = {
 			"syslog", &smk_syslog_ops, S_IRUGO|S_IWUSR},
+		[SMK_PTRACE] = {
+			"ptrace", &smk_ptrace_ops, S_IRUGO|S_IWUSR},
 		/* last one */
 			{""}
 	};