fsverity: constify fsverity_hash_alg

Now that fsverity_hash_alg doesn't have an embedded mempool, it can be
'const' almost everywhere.  Add it.

Link: https://lore.kernel.org/r/20230604022348.48658-1-ebiggers@kernel.orgSigned-off-by: Eric Biggers <ebiggers@google.com>

fs/verity/fsverity_private.h

@@ -33,7 +33,7 @@ struct fsverity_hash_alg {
 
 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */
 struct merkle_tree_params {
-	struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
+	const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
 	const u8 *hashstate;		/* initial hash state or NULL */
 	unsigned int digest_size;	/* same as hash_alg->digest_size */
 	unsigned int block_size;	/* size of data and tree blocks */
@@ -79,13 +79,13 @@ struct fsverity_info {
 
 extern struct fsverity_hash_alg fsverity_hash_algs[];
 
-struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
-						unsigned int num);
-const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
+const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
+						      unsigned int num);
+const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
 				      const u8 *salt, size_t salt_size);
 int fsverity_hash_block(const struct merkle_tree_params *params,
 			const struct inode *inode, const void *data, u8 *out);
-int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
+int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
 			 const void *data, size_t size, u8 *out);
 void __init fsverity_check_hash_algs(void);
 

fs/verity/hash_algs.c

@@ -39,8 +39,8 @@ static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
  *
  * Return: pointer to the hash alg on success, else an ERR_PTR()
  */
-struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
-						unsigned int num)
+const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
+						      unsigned int num)
 {
 	struct fsverity_hash_alg *alg;
 	struct crypto_shash *tfm;
@@ -108,7 +108,7 @@ struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
  * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
  *	   initial hash state on success or an ERR_PTR() on failure.
  */
-const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
+const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
 				      const u8 *salt, size_t salt_size)
 {
 	u8 *hashstate = NULL;
@@ -206,7 +206,7 @@ int fsverity_hash_block(const struct merkle_tree_params *params,
  *
  * Return: 0 on success, -errno on failure
  */
-int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
+int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
 			 const void *data, size_t size, u8 *out)
 {
 	return crypto_shash_tfm_digest(alg->tfm, data, size, out);

fs/verity/open.c

@@ -32,7 +32,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
 				     unsigned int log_blocksize,
 				     const u8 *salt, size_t salt_size)
 {
-	struct fsverity_hash_alg *hash_alg;
+	const struct fsverity_hash_alg *hash_alg;
 	int err;
 	u64 blocks;
 	u64 blocks_in_level[FS_VERITY_MAX_LEVELS];
@@ -158,7 +158,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
  * Compute the file digest by hashing the fsverity_descriptor excluding the
  * signature and with the sig_size field set to 0.
  */
-static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
+static int compute_file_digest(const struct fsverity_hash_alg *hash_alg,
 			       struct fsverity_descriptor *desc,
 			       u8 *file_digest)
 {