Smack: Implement lock security mode

Linux file locking does not follow the same rules
as other mechanisms. Even though it is a write operation
a process can set a read lock on files which it has open
only for read access. Two programs with read access to
a file can use read locks to communicate.

This is not acceptable in a Mandatory Access Control
environment. Smack treats setting a read lock as the
write operation that it is. Unfortunately, many programs
assume that setting a read lock is a read operation.
These programs are unhappy in the Smack environment.

This patch introduces a new access mode (lock) to address
this problem. A process with lock access to a file can
set a read lock. A process with write access to a file can
set a read lock or a write lock. This prevents a situation
where processes are granted write access just so they can
set read locks.

Targeted for git://git.gitorious.org/smack-next/kernel.git

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack.h

@@ -177,9 +177,13 @@ struct smk_port_label {
 #define SMACK_CIPSO_MAXCATNUM           184     /* 23 * 8 */
 
 /*
- * Flag for transmute access
+ * Flags for untraditional access modes.
+ * It shouldn't be necessary to avoid conflicts with definitions
+ * in fs.h, but do so anyway.
  */
-#define MAY_TRANSMUTE	64
+#define MAY_TRANSMUTE	0x00001000	/* Controls directory labeling */
+#define MAY_LOCK	0x00002000	/* Locks should be writes, but ... */
+
 /*
  * Just to make the common cases easier to deal with
  */
@@ -188,9 +192,9 @@ struct smk_port_label {
 #define MAY_NOT		0
 
 /*
- * Number of access types used by Smack (rwxat)
+ * Number of access types used by Smack (rwxatl)
  */
-#define SMK_NUM_ACCESS_TYPE 5
+#define SMK_NUM_ACCESS_TYPE 6
 
 /* SMACK data */
 struct smack_audit_data {

security/smack/smack_access.c

@@ -84,6 +84,8 @@ int log_policy = SMACK_AUDIT_DENIED;
  *
  * Do the object check first because that is more
  * likely to differ.
+ *
+ * Allowing write access implies allowing locking.
  */
 int smk_access_entry(char *subject_label, char *object_label,
 			struct list_head *rule_list)
@@ -99,6 +101,11 @@ int smk_access_entry(char *subject_label, char *object_label,
 		}
 	}
 
+	/*
+	 * MAY_WRITE implies MAY_LOCK.
+	 */
+	if ((may & MAY_WRITE) == MAY_WRITE)
+		may |= MAY_LOCK;
 	return may;
 }
 
@@ -245,6 +252,7 @@ out_audit:
 static inline void smack_str_from_perm(char *string, int access)
 {
 	int i = 0;
+
 	if (access & MAY_READ)
 		string[i++] = 'r';
 	if (access & MAY_WRITE)
@@ -255,6 +263,8 @@ static inline void smack_str_from_perm(char *string, int access)
 		string[i++] = 'a';
 	if (access & MAY_TRANSMUTE)
 		string[i++] = 't';
+	if (access & MAY_LOCK)
+		string[i++] = 'l';
 	string[i] = '\0';
 }
 /**

security/smack/smack_lsm.c

@@ -1146,7 +1146,7 @@ static int smack_file_ioctl(struct file *file, unsigned int cmd,
  * @file: the object
  * @cmd: unused
  *
- * Returns 0 if current has write access, error code otherwise
+ * Returns 0 if current has lock access, error code otherwise
  */
 static int smack_file_lock(struct file *file, unsigned int cmd)
 {
@@ -1154,7 +1154,7 @@ static int smack_file_lock(struct file *file, unsigned int cmd)
 
 	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);
 	smk_ad_setfield_u_fs_path(&ad, file->f_path);
-	return smk_curacc(file->f_security, MAY_WRITE, &ad);
+	return smk_curacc(file->f_security, MAY_LOCK, &ad);
 }
 
 /**
@@ -1178,8 +1178,13 @@ static int smack_file_fcntl(struct file *file, unsigned int cmd,
 
 	switch (cmd) {
 	case F_GETLK:
+		break;
 	case F_SETLK:
 	case F_SETLKW:
+		smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);
+		smk_ad_setfield_u_fs_path(&ad, file->f_path);
+		rc = smk_curacc(file->f_security, MAY_LOCK, &ad);
+		break;
 	case F_SETOWN:
 	case F_SETSIG:
 		smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);

security/smack/smackfs.c

@@ -139,7 +139,7 @@ const char *smack_cipso_option = SMACK_CIPSO_OPTION;
  * SMK_LOADLEN: Smack rule length
  */
 #define SMK_OACCESS	"rwxa"
-#define SMK_ACCESS	"rwxat"
+#define SMK_ACCESS	"rwxatl"
 #define SMK_OACCESSLEN	(sizeof(SMK_OACCESS) - 1)
 #define SMK_ACCESSLEN	(sizeof(SMK_ACCESS) - 1)
 #define SMK_OLOADLEN	(SMK_LABELLEN + SMK_LABELLEN + SMK_OACCESSLEN)
@@ -282,6 +282,10 @@ static int smk_perm_from_str(const char *string)
 		case 'T':
 			perm |= MAY_TRANSMUTE;
 			break;
+		case 'l':
+		case 'L':
+			perm |= MAY_LOCK;
+			break;
 		default:
 			return perm;
 		}
@@ -452,7 +456,7 @@ static ssize_t smk_write_rules_list(struct file *file, const char __user *buf,
 		/*
 		 * Minor hack for backward compatibility
 		 */
-		if (count != SMK_OLOADLEN && count != SMK_LOADLEN)
+		if (count < SMK_OLOADLEN || count > SMK_LOADLEN)
 			return -EINVAL;
 	} else {
 		if (count >= PAGE_SIZE) {
@@ -592,6 +596,8 @@ static void smk_rule_show(struct seq_file *s, struct smack_rule *srp, int max)
 		seq_putc(s, 'a');
 	if (srp->smk_access & MAY_TRANSMUTE)
 		seq_putc(s, 't');
+	if (srp->smk_access & MAY_LOCK)
+		seq_putc(s, 'l');
 
 	seq_putc(s, '\n');
 }