[PATCH v3 13/15] ima: add ima_inode_setxattr and ima_inode_removexattr

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

Based on xattr_permission comments, the restriction to modify
'security' xattr is left up to the underlying fs or lsm. Ensure
that not just anyone can modify or remove 'security.ima'.

Changelog:
  - Replace CAP_MAC_ADMIN with CAP_SYS_ADMIN
  - static inline ima_inode_setxattr()/ima_inode_removexattr() stubs
  - ima_protect_xattr should be static

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
---
 include/linux/ima.h               |   16 ++++++++++++++++
 security/integrity/ima/ima_main.c |   26 ++++++++++++++++++++++++++
 security/security.c               |    6 ++++++
 3 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index ce82e29..2f87cf8 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -20,6 +20,9 @@ extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
 extern void ima_counts_get(struct file *file);
 extern void ima_inode_post_setattr(struct dentry *dentry);
+extern int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
+		       const void *xattr_value, size_t xattr_value_len);
+extern int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name);
 
 #else
 static inline int ima_bprm_check(struct linux_binprm *bprm)
@@ -52,5 +55,18 @@ static inline void ima_inode_post_setattr(struct dentry *dentry)
 	return;
 }
 
+static inline int ima_inode_setxattr(struct dentry *dentry,
+				     const char *xattr_name,
+				     const void *xattr_value,
+				     size_t xattr_value_len)
+{
+	return 0;
+}
+
+static inline int ima_inode_removexattr(struct dentry *dentry,
+				        const char *xattr_name)
+{
+	return 0;
+}
 #endif /* CONFIG_IMA_H */
 #endif /* _LINUX_IMA_H */
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index d6132b9..6531765 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -372,6 +372,32 @@ void ima_inode_post_setattr(struct dentry *dentry)
 	return;
 }
 
+/*
+ * ima_protect_xattr - protect 'security.ima'
+ *
+ * Ensure that not just anyone can modify or remove 'security.ima'.
+ */
+static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
+			     const void *xattr_value, size_t xattr_value_len)
+{
+	if ((strcmp(xattr_name, XATTR_NAME_IMA) == 0)
+	    && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	return 0;
+}
+
+int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
+		       const void *xattr_value, size_t xattr_value_len)
+{
+	return ima_protect_xattr(dentry, xattr_name, xattr_value,
+				 xattr_value_len);
+}
+
+int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
+{
+	return ima_protect_xattr(dentry, xattr_name, NULL, 0);
+}
+
 static int __init init_ima(void)
 {
 	int error;
diff --git a/security/security.c b/security/security.c
index c373c5f..53c6285 100644
--- a/security/security.c
+++ b/security/security.c
@@ -556,6 +556,9 @@ int security_inode_setxattr(struct dentry *dentry, const char *name,
 	ret = security_ops->inode_setxattr(dentry, name, value, size, flags);
 	if (ret)
 		return ret;
+	ret = ima_inode_setxattr(dentry, name, value, size);
+	if (ret)
+		return ret;
 	return evm_inode_setxattr(dentry, name, value, size);
 }
 
@@ -591,6 +594,9 @@ int security_inode_removexattr(struct dentry *dentry, const char *name)
 	ret = security_ops->inode_removexattr(dentry, name);
 	if (ret)
 		return ret;
+	ret = ima_inode_removexattr(dentry, name);
+	if (ret)
+		return ret;
 	return evm_inode_removexattr(dentry, name);
 }
 
-- 
1.7.1.1