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-rw-r--r--fs/verity/measure.c57
1 files changed, 57 insertions, 0 deletions
diff --git a/fs/verity/measure.c b/fs/verity/measure.c
new file mode 100644
index 000000000000..05049b68c745
--- /dev/null
+++ b/fs/verity/measure.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/measure.c: ioctl to get a verity file's measurement
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/uaccess.h>
+
+/**
+ * fsverity_ioctl_measure() - get a verity file's measurement
+ *
+ * Retrieve the file measurement that the kernel is enforcing for reads from a
+ * verity file. See the "FS_IOC_MEASURE_VERITY" section of
+ * Documentation/filesystems/fsverity.rst for the documentation.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
+{
+ const struct inode *inode = file_inode(filp);
+ struct fsverity_digest __user *uarg = _uarg;
+ const struct fsverity_info *vi;
+ const struct fsverity_hash_alg *hash_alg;
+ struct fsverity_digest arg;
+
+ vi = fsverity_get_info(inode);
+ if (!vi)
+ return -ENODATA; /* not a verity file */
+ hash_alg = vi->tree_params.hash_alg;
+
+ /*
+ * The user specifies the digest_size their buffer has space for; we can
+ * return the digest if it fits in the available space. We write back
+ * the actual size, which may be shorter than the user-specified size.
+ */
+
+ if (get_user(arg.digest_size, &uarg->digest_size))
+ return -EFAULT;
+ if (arg.digest_size < hash_alg->digest_size)
+ return -EOVERFLOW;
+
+ memset(&arg, 0, sizeof(arg));
+ arg.digest_algorithm = hash_alg - fsverity_hash_algs;
+ arg.digest_size = hash_alg->digest_size;
+
+ if (copy_to_user(uarg, &arg, sizeof(arg)))
+ return -EFAULT;
+
+ if (copy_to_user(uarg->digest, vi->measurement, hash_alg->digest_size))
+ return -EFAULT;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);