fs-verity: add the hook for file ->setattr()

Add a function fsverity_prepare_setattr() which filesystems that support
fs-verity must call to deny truncates of verity files.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/fs/verity/open.c b/fs/verity/open.c
index 8013f77f907ebf38bbe40a581807b057eb27367c..2cb2fe8082bff435c27abb1055c8ee969aab904c 100644 (file)
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -295,6 +295,27 @@ int fsverity_file_open(struct inode *inode, struct file *filp)
 }
 EXPORT_SYMBOL_GPL(fsverity_file_open);
 
+/**
+ * fsverity_prepare_setattr() - prepare to change a verity inode's attributes
+ * @dentry: dentry through which the inode is being changed
+ * @attr: attributes to change
+ *
+ * Verity files are immutable, so deny truncates.  This isn't covered by the
+ * open-time check because sys_truncate() takes a path, not a file descriptor.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
+{
+       if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
+               pr_debug("Denying truncate of verity file (ino %lu)\n",
+                        d_inode(dentry)->i_ino);
+               return -EPERM;
+       }
+       return 0;
+}
+EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
+
 /**
  * fsverity_cleanup_inode() - free the inode's verity info, if present
  *

diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 09b04dab64520188028225f0b23b5d934231415b..cbd0f84e1620f7b4b0d20db9931f86b73203537d 100644 (file)
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -46,6 +46,7 @@ static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
 /* open.c */
 
 extern int fsverity_file_open(struct inode *inode, struct file *filp);
+extern int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 extern void fsverity_cleanup_inode(struct inode *inode);
 
 #else /* !CONFIG_FS_VERITY */
@@ -62,6 +63,12 @@ static inline int fsverity_file_open(struct inode *inode, struct file *filp)
        return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
 }
 
+static inline int fsverity_prepare_setattr(struct dentry *dentry,
+                                          struct iattr *attr)
+{
+       return IS_VERITY(d_inode(dentry)) ? -EOPNOTSUPP : 0;
+}
+
 static inline void fsverity_cleanup_inode(struct inode *inode)
 {
 }