From: Eric Biggers <ebiggers@xxxxxxxxxx>
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@xxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/verity/open.c | 21 +++++++++++++++++++++
include/linux/fsverity.h | 7 +++++++
2 files changed, 28 insertions(+)
diff --git a/fs/verity/open.c b/fs/verity/open.c
index 3a3bb27e23f5e3..21ae0ef254a695 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -296,6 +296,27 @@ 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 1372c236c8770c..cbcc358d073652 100644
--- 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)
{
}
--
2.22.0.410.gd8fdbe21b5-goog
