ima: add ima_inode_setxattr/removexattr function and calls

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 v1:
- Unless IMA-APPRAISE is configured, use stub ima_inode_removexattr()/setxattr()
  functions.  (Moved ima_inode_removexattr()/setxattr() to ima_appraise.c)

Changelog:
  - take i_mutex to fix locking (Dmitry Kasatkin)
  - ima_reset_appraise_flags should only be called when modifying or
    removing the 'security.ima' xattr. Requires CAP_SYS_ADMIN privilege.
    (Incorporated fix from Roberto Sassu)
  - Even if allowed to update security.ima, reset the appraisal flags,
    forcing re-appraisal.
  - 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>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

diff --git a/include/linux/ima.h b/include/linux/ima.h
index e2bfbb1..2c7223d 100644 (file)
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -44,10 +44,27 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
 
 #ifdef CONFIG_IMA_APPRAISE
 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 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_APPRAISE_H */
 #endif /* _LINUX_IMA_H */

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 681cb6e..becc7e0 100644 (file)
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -169,3 +169,60 @@ void ima_inode_post_setattr(struct dentry *dentry)
                rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
        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) {
+               if (!capable(CAP_SYS_ADMIN))
+                       return -EPERM;
+               return 1;
+       }
+       return 0;
+}
+
+static void ima_reset_appraise_flags(struct inode *inode)
+{
+       struct integrity_iint_cache *iint;
+
+       if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
+               return;
+
+       iint = integrity_iint_find(inode);
+       if (!iint)
+               return;
+
+       iint->flags &= ~(IMA_COLLECTED | IMA_APPRAISED | IMA_MEASURED);
+       return;
+}
+
+int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
+                      const void *xattr_value, size_t xattr_value_len)
+{
+       int result;
+
+       result = ima_protect_xattr(dentry, xattr_name, xattr_value,
+                                  xattr_value_len);
+       if (result == 1) {
+               ima_reset_appraise_flags(dentry->d_inode);
+               result = 0;
+       }
+       return result;
+}
+
+int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
+{
+       int result;
+
+       result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
+       if (result == 1) {
+               ima_reset_appraise_flags(dentry->d_inode);
+               result = 0;
+       }
+       return result;
+}

diff --git a/security/security.c b/security/security.c
index 68c1b9b..d23b435 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -573,6 +573,9 @@ 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);
 }
 
@@ -608,6 +611,9 @@ 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);
 }