[PATCH v3 18/24] LSM: Use lsmcontext in security_dentry_init_security

[Casey Schaufler]

Change the security_dentry_init_security() interface to
fill an lsmcontext structure instead of a void * data area
and a length. The lone caller of this interface is NFS4,
which may make copies of the data using its own mechanisms.
A rework of the nfs4 code to use the lsmcontext properly
is a significant project, so the coward's way out is taken,
and the lsmcontext data from security_dentry_init_security()
is copied, then released directly.

Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
---
 fs/nfs/nfs4proc.c        | 26 ++++++++++++++++----------
 include/linux/security.h |  7 +++----
 security/security.c      | 20 ++++++++++++++++----
 3 files changed, 35 insertions(+), 18 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index af1c0db29c39..952f805965bb 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -113,6 +113,7 @@ static inline struct nfs4_label *
 nfs4_label_init_security(struct inode *dir, struct dentry *dentry,
 	struct iattr *sattr, struct nfs4_label *label)
 {
+	struct lsmcontext context;
 	int err;
 
 	if (label == NULL)
@@ -122,21 +123,26 @@ nfs4_label_init_security(struct inode *dir, struct dentry *dentry,
 		return NULL;
 
 	err = security_dentry_init_security(dentry, sattr->ia_mode,
-				&dentry->d_name, (void **)&label->label, &label->len);
-	if (err == 0)
-		return label;
+					    &dentry->d_name, &context);
+
+	if (err)
+		return NULL;
+
+	label->label = kmemdup(context.context, context.len, GFP_KERNEL);
+	if (label->label == NULL)
+		label = NULL;
+	else
+		label->len = context.len;
+
+	security_release_secctx(&context);
+
+	return label;
 
-	return NULL;
 }
 static inline void
 nfs4_label_release_security(struct nfs4_label *label)
 {
-	struct lsmcontext scaff; /* scaffolding */
-
-	if (label) {
-		lsmcontext_init(&scaff, label->label, label->len, 0);
-		security_release_secctx(&scaff);
-	}
+	kfree(label->label);
 }
 static inline u32 *nfs4_bitmask(struct nfs_server *server, struct nfs4_label *label)
 {
diff --git a/include/linux/security.h b/include/linux/security.h
index 3cbe43db16f5..2a2785a4e752 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -348,8 +348,8 @@ int security_sb_clone_mnt_opts(const struct super_block *oldsb,
 int security_add_mnt_opt(const char *option, const char *val,
 				int len, void **mnt_opts);
 int security_dentry_init_security(struct dentry *dentry, int mode,
-					const struct qstr *name, void **ctx,
-					u32 *ctxlen);
+					const struct qstr *name,
+					struct lsmcontext *ctx);
 int security_dentry_create_files_as(struct dentry *dentry, int mode,
 					struct qstr *name,
 					const struct cred *old,
@@ -720,8 +720,7 @@ static inline void security_inode_free(struct inode *inode)
 static inline int security_dentry_init_security(struct dentry *dentry,
 						 int mode,
 						 const struct qstr *name,
-						 void **ctx,
-						 u32 *ctxlen)
+						 struct lsmcontext *ctx)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/security/security.c b/security/security.c
index f461ab3fb9c4..842ac65abc08 100644
--- a/security/security.c
+++ b/security/security.c
@@ -453,6 +453,8 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count,
 		 * secid in the lsmblob structure.
 		 */
 		if (hooks[i].head == &security_hook_heads.audit_rule_match ||
+		    hooks[i].head ==
+			&security_hook_heads.dentry_init_security ||
 		    hooks[i].head == &security_hook_heads.kernel_act_as ||
 		    hooks[i].head ==
 			&security_hook_heads.socket_getpeersec_dgram ||
@@ -1040,11 +1042,21 @@ void security_inode_free(struct inode *inode)
 }
 
 int security_dentry_init_security(struct dentry *dentry, int mode,
-					const struct qstr *name, void **ctx,
-					u32 *ctxlen)
+				  const struct qstr *name,
+				  struct lsmcontext *cp)
 {
-	return call_int_hook(dentry_init_security, -EOPNOTSUPP, dentry, mode,
-				name, ctx, ctxlen);
+	int *display = current->security;
+	struct security_hook_list *hp;
+
+	hlist_for_each_entry(hp, &security_hook_heads.dentry_init_security,
+			     list)
+		if (*display == 0 || *display == hp->slot) {
+			cp->slot = hp->slot;
+			return hp->hook.dentry_init_security(dentry, mode,
+					name, (void **)&cp->context, &cp->len);
+		}
+
+	return -EOPNOTSUPP;
 }
 EXPORT_SYMBOL(security_dentry_init_security);
 
-- 
2.20.1