Security: Add hook to calculate context based on a negative dentry.

There is a time where we need to calculate a context without the
inode having been created yet. To do this we take the negative dentry and
calculate a context based on the process and the parent directory contexts.

Acked-by: Eric Paris <eparis@redhat.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Matthew N. Dodd <Matthew.Dodd@sparta.com>
Signed-off-by: Miguel Rodel Felipe <Rodel_FM@dsi.a-star.edu.sg>
Signed-off-by: Phua Eu Gene <PHUA_Eu_Gene@dsi.a-star.edu.sg>
Signed-off-by: Khin Mi Mi Aung <Mi_Mi_AUNG@dsi.a-star.edu.sg>
Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/security.h

@@ -26,6 +26,7 @@
 #include <linux/capability.h>
 #include <linux/slab.h>
 #include <linux/err.h>
+#include <linux/string.h>
 
 struct linux_binprm;
 struct cred;
@@ -306,6 +307,15 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *	Parse a string of security data filling in the opts structure
  *	@options string containing all mount options known by the LSM
  *	@opts binary data structure usable by the LSM
+ * @dentry_init_security:
+ *	Compute a context for a dentry as the inode is not yet available
+ *	since NFSv4 has no label backed by an EA anyway.
+ *	@dentry dentry to use in calculating the context.
+ *	@mode mode used to determine resource type.
+ *	@name name of the last path component used to create file
+ *	@ctx pointer to place the pointer to the resulting context in.
+ *	@ctxlen point to place the length of the resulting context.
+ *
  *
  * Security hooks for inode operations.
  *
@@ -1443,6 +1453,10 @@ struct security_operations {
 	int (*sb_clone_mnt_opts) (const struct super_block *oldsb,
 				   struct super_block *newsb);
 	int (*sb_parse_opts_str) (char *options, struct security_mnt_opts *opts);
+	int (*dentry_init_security) (struct dentry *dentry, int mode,
+					struct qstr *name, void **ctx,
+					u32 *ctxlen);
+
 
 #ifdef CONFIG_SECURITY_PATH
 	int (*path_unlink) (struct path *dir, struct dentry *dentry);
@@ -1729,6 +1743,9 @@ int security_sb_set_mnt_opts(struct super_block *sb, struct security_mnt_opts *o
 int security_sb_clone_mnt_opts(const struct super_block *oldsb,
 				struct super_block *newsb);
 int security_sb_parse_opts_str(char *options, struct security_mnt_opts *opts);
+int security_dentry_init_security(struct dentry *dentry, int mode,
+					struct qstr *name, void **ctx,
+					u32 *ctxlen);
 
 int security_inode_alloc(struct inode *inode);
 void security_inode_free(struct inode *inode);
@@ -2035,6 +2052,16 @@ static inline int security_inode_alloc(struct inode *inode)
 static inline void security_inode_free(struct inode *inode)
 { }
 
+static inline int security_dentry_init_security(struct dentry *dentry,
+						 int mode,
+						 struct qstr *name,
+						 void **ctx,
+						 u32 *ctxlen)
+{
+	return -EOPNOTSUPP;
+}
+
+
 static inline int security_inode_init_security(struct inode *inode,
 						struct inode *dir,
 						const struct qstr *qstr,

security/capability.c

@@ -109,6 +109,13 @@ static int cap_sb_parse_opts_str(char *options, struct security_mnt_opts *opts)
 	return 0;
 }
 
+static int cap_dentry_init_security(struct dentry *dentry, int mode,
+					struct qstr *name, void **ctx,
+					u32 *ctxlen)
+{
+	return 0;
+}
+
 static int cap_inode_alloc_security(struct inode *inode)
 {
 	return 0;
@@ -931,6 +938,7 @@ void __init security_fixup_ops(struct security_operations *ops)
 	set_to_cap_if_null(ops, sb_set_mnt_opts);
 	set_to_cap_if_null(ops, sb_clone_mnt_opts);
 	set_to_cap_if_null(ops, sb_parse_opts_str);
+	set_to_cap_if_null(ops, dentry_init_security);
 	set_to_cap_if_null(ops, inode_alloc_security);
 	set_to_cap_if_null(ops, inode_free_security);
 	set_to_cap_if_null(ops, inode_init_security);

security/security.c

@@ -12,6 +12,7 @@
  */
 
 #include <linux/capability.h>
+#include <linux/dcache.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
@@ -324,6 +325,15 @@ void security_inode_free(struct inode *inode)
 	security_ops->inode_free_security(inode);
 }
 
+int security_dentry_init_security(struct dentry *dentry, int mode,
+					struct qstr *name, void **ctx,
+					u32 *ctxlen)
+{
+	return security_ops->dentry_init_security(dentry, mode, name,
+							ctx, ctxlen);
+}
+EXPORT_SYMBOL(security_dentry_init_security);
+
 int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 const initxattrs initxattrs, void *fs_data)

security/selinux/hooks.c

@@ -2515,6 +2515,40 @@ static void selinux_inode_free_security(struct inode *inode)
 	inode_free_security(inode);
 }
 
+static int selinux_dentry_init_security(struct dentry *dentry, int mode,
+					struct qstr *name, void **ctx,
+					u32 *ctxlen)
+{
+	const struct cred *cred = current_cred();
+	struct task_security_struct *tsec;
+	struct inode_security_struct *dsec;
+	struct superblock_security_struct *sbsec;
+	struct inode *dir = dentry->d_parent->d_inode;
+	u32 newsid;
+	int rc;
+
+	tsec = cred->security;
+	dsec = dir->i_security;
+	sbsec = dir->i_sb->s_security;
+
+	if (tsec->create_sid && sbsec->behavior != SECURITY_FS_USE_MNTPOINT) {
+		newsid = tsec->create_sid;
+	} else {
+		rc = security_transition_sid(tsec->sid, dsec->sid,
+					     inode_mode_to_security_class(mode),
+					     name,
+					     &newsid);
+		if (rc) {
+			printk(KERN_WARNING
+				"%s: security_transition_sid failed, rc=%d\n",
+			       __func__, -rc);
+			return rc;
+		}
+	}
+
+	return security_sid_to_context(newsid, (char **)ctx, ctxlen);
+}
+
 static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 				       const struct qstr *qstr, char **name,
 				       void **value, size_t *len)
@@ -5562,6 +5596,7 @@ static struct security_operations selinux_ops = {
 	.sb_clone_mnt_opts =		selinux_sb_clone_mnt_opts,
 	.sb_parse_opts_str = 		selinux_parse_opts_str,
 
+	.dentry_init_security =		selinux_dentry_init_security,
 
 	.inode_alloc_security =		selinux_inode_alloc_security,
 	.inode_free_security =		selinux_inode_free_security,