security: Introduce inode_post_setattr hook

In preparation for moving IMA and EVM to the LSM infrastructure, introduce
the inode_post_setattr hook.

At inode_setattr hook, EVM verifies the file's existing HMAC value. At
inode_post_setattr, EVM re-calculates the file's HMAC based on the modified
file attributes and other file metadata.

Other LSMs could similarly take some action after successful file attribute
change.

The new hook cannot return an error and cannot cause the operation to be
reverted.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/fs/attr.c b/fs/attr.c
index adeba0ec40f1ec555e6d442aee69e1e941ace5e7..990e1b3a3c9117361152191ec59636a130ba288b 100644 (file)
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -502,6 +502,7 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
 
        if (!error) {
                fsnotify_change(dentry, ia_valid);
+               security_inode_post_setattr(idmap, dentry, ia_valid);
                ima_inode_post_setattr(idmap, dentry, ia_valid);
                evm_inode_post_setattr(idmap, dentry, ia_valid);
        }

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index b00b16d58413332078b1e0f0dd7b1721867f1594..a0e9e48015a4f34832528d685b5ff9afc56bf1b7 100644 (file)
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -137,6 +137,8 @@ LSM_HOOK(int, 0, inode_follow_link, struct dentry *dentry, struct inode *inode,
 LSM_HOOK(int, 0, inode_permission, struct inode *inode, int mask)
 LSM_HOOK(int, 0, inode_setattr, struct mnt_idmap *idmap, struct dentry *dentry,
         struct iattr *attr)
+LSM_HOOK(void, LSM_RET_VOID, inode_post_setattr, struct mnt_idmap *idmap,
+        struct dentry *dentry, int ia_valid)
 LSM_HOOK(int, 0, inode_getattr, const struct path *path)
 LSM_HOOK(int, 0, inode_setxattr, struct mnt_idmap *idmap,
         struct dentry *dentry, const char *name, const void *value,

diff --git a/include/linux/security.h b/include/linux/security.h
index d0eb20f90b264a3fdf96bfc60b28e2091638edd8..56c841aa399421dc5763aa0286a080d612865547 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -361,6 +361,8 @@ int security_inode_follow_link(struct dentry *dentry, struct inode *inode,
 int security_inode_permission(struct inode *inode, int mask);
 int security_inode_setattr(struct mnt_idmap *idmap,
                           struct dentry *dentry, struct iattr *attr);
+void security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+                                int ia_valid);
 int security_inode_getattr(const struct path *path);
 int security_inode_setxattr(struct mnt_idmap *idmap,
                            struct dentry *dentry, const char *name,
@@ -879,6 +881,11 @@ static inline int security_inode_setattr(struct mnt_idmap *idmap,
        return 0;
 }
 
+static inline void
+security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+                           int ia_valid)
+{ }
+
 static inline int security_inode_getattr(const struct path *path)
 {
        return 0;

diff --git a/security/security.c b/security/security.c
index 9dc601d459608c613c5e3a018fb79b45f106f637..56527d5415e23bcbf2d613a51321526012885387 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -2222,6 +2222,22 @@ int security_inode_setattr(struct mnt_idmap *idmap,
 }
 EXPORT_SYMBOL_GPL(security_inode_setattr);
 
+/**
+ * security_inode_post_setattr() - Update the inode after a setattr operation
+ * @idmap: idmap of the mount
+ * @dentry: file
+ * @ia_valid: file attributes set
+ *
+ * Update inode security field after successful setting file attributes.
+ */
+void security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+                                int ia_valid)
+{
+       if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
+               return;
+       call_void_hook(inode_post_setattr, idmap, dentry, ia_valid);
+}
+
 /**
  * security_inode_getattr() - Check if getting file attributes is allowed
  * @path: file