linux-kernel - [RFC][PATCH v3a 07/11] fsverity: Introduce fsverity_get

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Date:   Thu, 27 Jan 2022 19:46:11 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     <linux-integrity@...r.kernel.org>
CC:     <zohar@...ux.ibm.com>, <ebiggers@...nel.org>,
        <stefanb@...ux.ibm.com>, <linux-fscrypt@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: [RFC][PATCH v3a 07/11] fsverity: Introduce fsverity_get_signature()

Get the signature of an fsverity-protected file.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 fs/verity/measure.c      | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/fsverity.h |  7 +++++++
 2 files changed, 45 insertions(+)

diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index 7afe4274ecb0..679e2ddae62c 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -142,3 +142,41 @@ ssize_t fsverity_get_formatted_digest(struct inode *inode,
 
 	return sizeof(*d) + hash_alg->digest_size;
 }
+
+/**
+ * fsverity_get_signature() - get a verity file's signature
+ * @inode: inode to get signature of
+ * @signature: (out) pointer to the signature
+ *
+ * Return the file signature of an fsverity-protected file.
+ *
+ * Return: written bytes on success, -errno on failure
+ */
+ssize_t fsverity_get_signature(struct inode *inode, u8 **signature)
+{
+	const struct fsverity_info *vi;
+	struct fsverity_descriptor *desc;
+	size_t desc_size;
+	int err, signature_size;
+
+	vi = fsverity_get_info(inode);
+	if (!vi)
+		return -ENODATA; /* not a verity file */
+
+	err = fsverity_get_descriptor(inode, &desc, &desc_size);
+	if (err)
+		return err;
+
+	signature_size = le32_to_cpu(desc->sig_size);
+
+	*signature = kmemdup(desc->signature, signature_size, GFP_KERNEL);
+
+	kfree(desc);
+
+	if (!*signature)
+		return -ENOMEM;
+
+	pr_debug("file signature %*phN\n", signature_size, *signature);
+
+	return signature_size;
+}
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 17ae313ed8f4..5ad7921f3589 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -147,6 +147,7 @@ int fsverity_get_digest(struct inode *inode,
 ssize_t fsverity_get_formatted_digest(struct inode *inode,
 			u8 formatted_digest[FS_VERITY_MAX_FMT_DIGEST_SIZE],
 			enum hash_algo *alg);
+ssize_t fsverity_get_signature(struct inode *inode, u8 **signature);
 
 /* open.c */
 
@@ -200,6 +201,12 @@ static inline ssize_t fsverity_get_formatted_digest(struct inode *inode,
 	return -EOPNOTSUPP;
 }
 
+static inline ssize_t fsverity_get_signature(struct inode *inode,
+					     u8 **signature)
+{
+	return -EOPNOTSUPP;
+}
+
 /* open.c */
 
 static inline int fsverity_file_open(struct inode *inode, struct file *filp)
-- 
2.32.0