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

Add the fsverity_file_open() function, which prepares an fs-verity file
to be read from.  If not already done, it loads the fs-verity descriptor
from the filesystem and sets up an fsverity_info structure for the inode
which describes the Merkle tree and contains the file measurement.  It
also denies all attempts to open verity files for writing.

This commit also begins the include/linux/fsverity.h header, which
declares the interface between fs/verity/ and filesystems.

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

1 files changed, 52 insertions, 2 deletions

diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index 9697aaebb5dc..c79746ff335e 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -15,8 +15,7 @@
 #define pr_fmt(fmt) "fs-verity: " fmt
 
 #include <crypto/sha.h>
-#include <linux/fs.h>
-#include <uapi/linux/fsverity.h>
+#include <linux/fsverity.h>
 
 struct ahash_request;
 
@@ -59,6 +58,40 @@ struct merkle_tree_params {
 	u64 level_start[FS_VERITY_MAX_LEVELS];
 };
 
+/**
+ * fsverity_info - cached verity metadata for an inode
+ *
+ * When a verity file is first opened, an instance of this struct is allocated
+ * and stored in ->i_verity_info; it remains until the inode is evicted.  It
+ * caches information about the Merkle tree that's needed to efficiently verify
+ * data read from the file.  It also caches the file measurement.  The Merkle
+ * tree pages themselves are not cached here, but the filesystem may cache them.
+ */
+struct fsverity_info {
+	struct merkle_tree_params tree_params;
+	u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
+	u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
+	const struct inode *inode;
+};
+
+/*
+ * Merkle tree properties.  The file measurement is the hash of this structure.
+ */
+struct fsverity_descriptor {
+	__u8 version;		/* must be 1 */
+	__u8 hash_algorithm;	/* Merkle tree hash algorithm */
+	__u8 log_blocksize;	/* log2 of size of data and tree blocks */
+	__u8 salt_size;		/* size of salt in bytes; 0 if none */
+	__le32 sig_size;	/* reserved, must be 0 */
+	__le64 data_size;	/* size of file the Merkle tree is built over */
+	__u8 root_hash[64];	/* Merkle tree root hash */
+	__u8 salt[32];		/* salt prepended to each hashed block */
+	__u8 __reserved[144];	/* must be 0's */
+};
+
+/* Arbitrary limit to bound the kmalloc() size.  Can be changed. */
+#define FS_VERITY_MAX_DESCRIPTOR_SIZE	16384
+
 /* hash_algs.c */
 
 extern struct fsverity_hash_alg fsverity_hash_algs[];
@@ -85,4 +118,21 @@ fsverity_msg(const struct inode *inode, const char *level,
 #define fsverity_err(inode, fmt, ...)		\
 	fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
 
+/* open.c */
+
+int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
+				     const struct inode *inode,
+				     unsigned int hash_algorithm,
+				     unsigned int log_blocksize,
+				     const u8 *salt, size_t salt_size);
+
+struct fsverity_info *fsverity_create_info(const struct inode *inode,
+					   const void *desc, size_t desc_size);
+
+void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
+
+void fsverity_free_info(struct fsverity_info *vi);
+
+int __init fsverity_init_info_cache(void);
+
 #endif /* _FSVERITY_PRIVATE_H */