Smack: recursive tramsmute

The transmuting directory feature of Smack requires that
the transmuting attribute be explicitly set in all cases.
It seems the users of this facility would expect that the
transmuting attribute be inherited by subdirectories that
are created in a transmuting directory. This does not seem
to add any additional complexity to the understanding of
how the system works.
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack.h

@@ -66,6 +66,7 @@ struct task_smack {
 
 #define	SMK_INODE_INSTANT	0x01	/* inode is instantiated */
 #define	SMK_INODE_TRANSMUTE	0x02	/* directory is transmuting */
+#define	SMK_INODE_CHANGED	0x04	/* smack was transmuted */
 
 /*
  * A label access rule.

security/smack/smack_lsm.c

@@ -556,6 +556,7 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 				     void **value, size_t *len)
 {
 	struct smack_known *skp;
+	struct inode_smack *issp = inode->i_security;
 	char *csp = smk_of_current();
 	char *isp = smk_of_inode(inode);
 	char *dsp = smk_of_inode(dir);
@@ -577,10 +578,13 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 		 * If the access rule allows transmutation and
 		 * the directory requests transmutation then
 		 * by all means transmute.
+		 * Mark the inode as changed.
 		 */
 		if (may > 0 && ((may & MAY_TRANSMUTE) != 0) &&
-		    smk_inode_transmutable(dir))
+		    smk_inode_transmutable(dir)) {
 			isp = dsp;
+			issp->smk_flags |= SMK_INODE_CHANGED;
+		}
 
 		*value = kstrdup(isp, GFP_KERNEL);
 		if (*value == NULL)
@@ -2552,6 +2556,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 	char *final;
 	char trattr[TRANS_TRUE_SIZE];
 	int transflag = 0;
+	int rc;
 	struct dentry *dp;
 
 	if (inode == NULL)
@@ -2670,17 +2675,38 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
 		 */
 		dp = dget(opt_dentry);
 		fetched = smk_fetch(XATTR_NAME_SMACK, inode, dp);
-		if (fetched != NULL) {
+		if (fetched != NULL)
 			final = fetched;
-			if (S_ISDIR(inode->i_mode)) {
-				trattr[0] = '\0';
-				inode->i_op->getxattr(dp,
+
+		/*
+		 * Transmuting directory
+		 */
+		if (S_ISDIR(inode->i_mode)) {
+			/*
+			 * If this is a new directory and the label was
+			 * transmuted when the inode was initialized
+			 * set the transmute attribute on the directory
+			 * and mark the inode.
+			 *
+			 * If there is a transmute attribute on the
+			 * directory mark the inode.
+			 */
+			if (isp->smk_flags & SMK_INODE_CHANGED) {
+				isp->smk_flags &= ~SMK_INODE_CHANGED;
+				rc = inode->i_op->setxattr(dp,
 					XATTR_NAME_SMACKTRANSMUTE,
-					trattr, TRANS_TRUE_SIZE);
-				if (strncmp(trattr, TRANS_TRUE,
-					    TRANS_TRUE_SIZE) == 0)
-					transflag = SMK_INODE_TRANSMUTE;
+					TRANS_TRUE, TRANS_TRUE_SIZE,
+					0);
+			} else {
+				rc = inode->i_op->getxattr(dp,
+					XATTR_NAME_SMACKTRANSMUTE, trattr,
+					TRANS_TRUE_SIZE);
+				if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
+						       TRANS_TRUE_SIZE) != 0)
+					rc = -EINVAL;
 			}
+			if (rc >= 0)
+				transflag = SMK_INODE_TRANSMUTE;
 		}
 		isp->smk_task = smk_fetch(XATTR_NAME_SMACKEXEC, inode, dp);
 		isp->smk_mmap = smk_fetch(XATTR_NAME_SMACKMMAP, inode, dp);