[PATCH v3 3/6] security: Pass xattrs allocated by LSMs to the inode_init_security hook

[Roberto Sassu]

In preparation for moving EVM to the LSM infrastructure, this patch
replaces the name, value, len triple with the xattr array pointer provided
by security_inode_init_security(), and the base slot in the xattr array
where LSMs can write xattrs.

This patch also introduces the new helper lsm_find_xattr_slot(), to help
LSMs find available slots in the xattr array (with a subsequent patch it
will be possible to reserve more than one slot). The helper takes three
arguments: the xattr array, the pointer of the base slot, whose value is
incremented each time the helper is called, and the end slot so that the
helper does not return a slot outside the array.

Finally, this patch modifies also SELinux and Smack to use the new helper.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 include/linux/lsm_hook_defs.h |  4 ++--
 include/linux/lsm_hooks.h     | 21 ++++++++++++++++++---
 security/security.c           | 15 ++++++---------
 security/selinux/hooks.c      | 15 ++++++++-------
 security/smack/smack_lsm.c    | 24 +++++++++++++-----------
 5 files changed, 47 insertions(+), 32 deletions(-)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 477a597db013..20f91e93f511 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -111,8 +111,8 @@ LSM_HOOK(int, 0, path_notify, const struct path *path, u64 mask,
 LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode)
 LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
 LSM_HOOK(int, 0, inode_init_security, struct inode *inode,
-	 struct inode *dir, const struct qstr *qstr, const char **name,
-	 void **value, size_t *len)
+	 struct inode *dir, const struct qstr *qstr, struct xattr *xattrs,
+	 int *base_slot, void *fs_data)
 LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
 	 const struct qstr *name, const struct inode *context_inode)
 LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index c5498f5174ce..197d6662b262 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -27,6 +27,7 @@
 
 #include <linux/security.h>
 #include <linux/init.h>
+#include <linux/xattr.h>
 #include <linux/rculist.h>
 
 /**
@@ -227,9 +228,13 @@
  *	@inode contains the inode structure of the newly created inode.
  *	@dir contains the inode structure of the parent directory.
  *	@qstr contains the last path component of the new object
- *	@name will be set to the allocated name suffix (e.g. selinux).
- *	@value will be set to the allocated attribute value.
- *	@len will be set to the length of the value.
+ *	@xattrs contains the full array of xattrs allocated by LSMs where
+ *	->name will be set to the allocated name suffix (e.g. selinux).
+ *	->value will be set to the allocated attribute value.
+ *	->len will be set to the length of the value.
+ *	@base_slot contains the position in @xattrs from where xattrs
+ *	can be written.
+ *	@fs_data contains filesystem-specific data.
  *	Returns 0 if @name and @value have been successfully set,
  *	-EOPNOTSUPP if no security attribute is needed, or
  *	-ENOMEM on memory allocation failure.
@@ -1660,5 +1665,15 @@ static inline void security_delete_hooks(struct security_hook_list *hooks,
 #endif /* CONFIG_SECURITY_WRITABLE_HOOKS */
 
 extern int lsm_inode_alloc(struct inode *inode);
+static inline struct xattr *lsm_find_xattr_slot(struct xattr *xattrs,
+						int *base_slot, int end_slot)
+{
+	if (!xattrs)
+		return xattrs;
+
+	if (*base_slot >= end_slot)
+		return NULL;
 
+	return xattrs + (*base_slot)++;
+}
 #endif /* ! __LINUX_LSM_HOOKS_H */
diff --git a/security/security.c b/security/security.c
index 692a148ce764..527a18fd6742 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1043,26 +1043,23 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const initxattrs initxattrs, void *fs_data)
 {
 	struct xattr new_xattrs[MAX_LSM_EVM_XATTR + 1];
-	struct xattr *lsm_xattr, *evm_xattr, *xattr;
-	int ret;
+	struct xattr *xattr;
+	int ret, base_slot = 0;
 
 	if (unlikely(IS_PRIVATE(inode)))
 		return 0;
 
 	if (!initxattrs)
 		return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
-				     dir, qstr, NULL, NULL, NULL);
+				     dir, qstr, NULL, &base_slot, fs_data);
 	memset(new_xattrs, 0, sizeof(new_xattrs));
-	lsm_xattr = new_xattrs;
 	ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
-						&lsm_xattr->name,
-						&lsm_xattr->value,
-						&lsm_xattr->value_len);
+			    new_xattrs, &base_slot, fs_data);
 	if (ret)
 		goto out;
 
-	evm_xattr = lsm_xattr + 1;
-	ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr);
+	ret = evm_inode_init_security(inode, new_xattrs,
+				      new_xattrs + base_slot);
 	if (ret)
 		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ddd097790d47..6319417129af 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2916,11 +2916,13 @@ static int selinux_dentry_create_files_as(struct dentry *dentry, int mode,
 
 static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 				       const struct qstr *qstr,
-				       const char **name,
-				       void **value, size_t *len)
+				       struct xattr *xattrs, int *base_slot,
+				       void *fs_data)
 {
 	const struct task_security_struct *tsec = selinux_cred(current_cred());
 	struct superblock_security_struct *sbsec;
+	struct xattr *xattr = lsm_find_xattr_slot(xattrs, base_slot,
+						  *base_slot + 1);
 	u32 newsid, clen;
 	int rc;
 	char *context;
@@ -2947,16 +2949,15 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
 	    !(sbsec->flags & SBLABEL_MNT))
 		return -EOPNOTSUPP;
 
-	if (name)
-		*name = XATTR_SELINUX_SUFFIX;
+	if (xattr) {
+		xattr->name = XATTR_SELINUX_SUFFIX;
 
-	if (value && len) {
 		rc = security_sid_to_context_force(&selinux_state, newsid,
 						   &context, &clen);
 		if (rc)
 			return rc;
-		*value = context;
-		*len = clen;
+		xattr->value = context;
+		xattr->value_len = clen;
 	}
 
 	return 0;
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 12a45e61c1a5..53e32cde09fb 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -962,26 +962,28 @@ static int smack_inode_alloc_security(struct inode *inode)
  * @inode: the newly created inode
  * @dir: containing directory object
  * @qstr: unused
- * @name: where to put the attribute name
- * @value: where to put the attribute value
- * @len: where to put the length of the attribute
+ * @xattrs: where to put the attribute
+ * @base_slot: where to start to write in @xattrs
+ * @fs_data: unused
  *
  * Returns 0 if it all works out, -ENOMEM if there's no memory
  */
 static int smack_inode_init_security(struct inode *inode, struct inode *dir,
-				     const struct qstr *qstr, const char **name,
-				     void **value, size_t *len)
+				     const struct qstr *qstr,
+				     struct xattr *xattrs, int *base_slot,
+				     void *fs_data)
 {
 	struct inode_smack *issp = smack_inode(inode);
 	struct smack_known *skp = smk_of_current();
 	struct smack_known *isp = smk_of_inode(inode);
 	struct smack_known *dsp = smk_of_inode(dir);
+	struct xattr *xattr = lsm_find_xattr_slot(xattrs, base_slot,
+						  *base_slot + 1);
 	int may;
 
-	if (name)
-		*name = XATTR_SMACK_SUFFIX;
+	if (xattr) {
+		xattr->name = XATTR_SMACK_SUFFIX;
 
-	if (value && len) {
 		rcu_read_lock();
 		may = smk_access_entry(skp->smk_known, dsp->smk_known,
 				       &skp->smk_rules);
@@ -999,11 +1001,11 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
 			issp->smk_flags |= SMK_INODE_CHANGED;
 		}
 
-		*value = kstrdup(isp->smk_known, GFP_NOFS);
-		if (*value == NULL)
+		xattr->value = kstrdup(isp->smk_known, GFP_NOFS);
+		if (xattr->value == NULL)
 			return -ENOMEM;
 
-		*len = strlen(isp->smk_known);
+		xattr->value_len = strlen(isp->smk_known);
 	}
 
 	return 0;
-- 
2.25.1