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>

Documentation/security/Smack.txt

@@ -204,6 +204,16 @@ onlycap
 	these capabilities are effective at for processes with any
 	label. The value is set by writing the desired label to the
 	file or cleared by writing "-" to the file.
+ptrace
+	This is used to define the current ptrace policy
+	0 - default: this is the policy that relies on smack access rules.
+	    For the PTRACE_READ a subject needs to have a read access on
+	    object. For the PTRACE_ATTACH a read-write access is required.
+	1 - exact: this is the policy that limits PTRACE_ATTACH. Attach is
+	    only allowed when subject's and object's labels are equal.
+	    PTRACE_READ is not affected. Can be overriden with CAP_SYS_PTRACE.
+	2 - draconian: this policy behaves like the 'exact' above with an
+	    exception that it can't be overriden with CAP_SYS_PTRACE.
 revoke-subject
 	Writing a Smack label here sets the access to '-' for all access
 	rules with that subject label.

security/smack/smack.h

@@ -176,6 +176,14 @@ struct smk_port_label {
  */
 #define SMACK_CIPSO_MAXCATNUM           184     /* 23 * 8 */
 
+/*
+ * Ptrace rules
+ */
+#define SMACK_PTRACE_DEFAULT	0
+#define SMACK_PTRACE_EXACT	1
+#define SMACK_PTRACE_DRACONIAN	2
+#define SMACK_PTRACE_MAX	SMACK_PTRACE_DRACONIAN
+
 /*
  * Flags for untraditional access modes.
  * It shouldn't be necessary to avoid conflicts with definitions
@@ -245,6 +253,7 @@ extern struct smack_known *smack_net_ambient;
 extern struct smack_known *smack_onlycap;
 extern struct smack_known *smack_syslog_label;
 extern const char *smack_cipso_option;
+extern int smack_ptrace_rule;
 
 extern struct smack_known smack_known_floor;
 extern struct smack_known smack_known_hat;

security/smack/smack_access.c

@@ -304,6 +304,9 @@ static void smack_log_callback(struct audit_buffer *ab, void *a)
 	audit_log_untrustedstring(ab, sad->subject);
 	audit_log_format(ab, " object=");
 	audit_log_untrustedstring(ab, sad->object);
+	if (sad->request[0] == '\0')
+		audit_log_format(ab, " labels_differ");
+	else
 		audit_log_format(ab, " requested=%s", sad->request);
 }
 

security/smack/smack_lsm.c

@@ -178,7 +178,8 @@ static inline unsigned int smk_ptrace_mode(unsigned int mode)
 /**
  * smk_ptrace_rule_check - helper for ptrace access
  * @tracer: tracer process
- * @tracee_label: label of the process that's about to be traced
+ * @tracee_label: label of the process that's about to be traced,
+ *                the pointer must originate from smack structures
  * @mode: ptrace attachment mode (PTRACE_MODE_*)
  * @func: name of the function that called us, used for audit
  *
@@ -201,6 +202,25 @@ static int smk_ptrace_rule_check(struct task_struct *tracer, char *tracee_label,
 	tsp = task_security(tracer);
 	skp = smk_of_task(tsp);
 
+	if ((mode & PTRACE_MODE_ATTACH) &&
+	    (smack_ptrace_rule == SMACK_PTRACE_EXACT ||
+	     smack_ptrace_rule == SMACK_PTRACE_DRACONIAN)) {
+		if (skp->smk_known == tracee_label)
+			rc = 0;
+		else if (smack_ptrace_rule == SMACK_PTRACE_DRACONIAN)
+			rc = -EACCES;
+		else if (capable(CAP_SYS_PTRACE))
+			rc = 0;
+		else
+			rc = -EACCES;
+
+		if (saip)
+			smack_log(skp->smk_known, tracee_label, 0, rc, saip);
+
+		return rc;
+	}
+
+	/* In case of rule==SMACK_PTRACE_DEFAULT or mode==PTRACE_MODE_READ */
 	rc = smk_tskacc(tsp, tracee_label, smk_ptrace_mode(mode), saip);
 	return rc;
 }

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 */
 			{""}
 	};