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>

1 files changed, 57 insertions, 0 deletions

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 681cb6e72257..becc7e09116d 100644
--- 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;
+}