smb: client: Use MD5 library for M-F symlink hashing

Convert parse_mf_symlink() and format_mf_symlink() to use the MD5
library instead of a "md5" crypto_shash.  This is simpler and faster.
With the library there's no need to allocate memory, no need to handle
errors, and the MD5 code is accessed directly without inefficient
indirect calls and other unnecessary API overhead.

This also fixes an issue where these functions did not work on kernels
booted in FIPS mode.  The use of MD5 here is for data integrity rather
than a security purpose, so it can use a non-FIPS-approved algorithm.

Reviewed-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Eric Biggers

fs/smb/client/Kconfig

@@ -16,6 +16,7 @@ config CIFS
 	select CRYPTO_ECB
 	select CRYPTO_AES
 	select CRYPTO_LIB_ARC4
+	select CRYPTO_LIB_MD5
 	select CRYPTO_LIB_SHA256
 	select CRYPTO_LIB_SHA512
 	select KEYS

fs/smb/client/link.c

@@ -5,6 +5,7 @@
  *   Author(s): Steve French (sfrench@us.ibm.com)
  *
  */
+#include <crypto/md5.h>
 #include <linux/fs.h>
 #include <linux/stat.h>
 #include <linux/slab.h>
@@ -36,23 +37,6 @@
 #define CIFS_MF_SYMLINK_MD5_FORMAT "%16phN\n"
 #define CIFS_MF_SYMLINK_MD5_ARGS(md5_hash) md5_hash
 
-static int
-symlink_hash(unsigned int link_len, const char *link_str, u8 *md5_hash)
-{
-	int rc;
-	struct shash_desc *md5 = NULL;
-
-	rc = cifs_alloc_hash("md5", &md5);
-	if (rc)
-		return rc;
-
-	rc = crypto_shash_digest(md5, link_str, link_len, md5_hash);
-	if (rc)
-		cifs_dbg(VFS, "%s: Could not generate md5 hash\n", __func__);
-	cifs_free_hash(&md5);
-	return rc;
-}
-
 static int
 parse_mf_symlink(const u8 *buf, unsigned int buf_len, unsigned int *_link_len,
 		 char **_link_str)
@@ -77,11 +61,7 @@ parse_mf_symlink(const u8 *buf, unsigned int buf_len, unsigned int *_link_len,
 	if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)
 		return -EINVAL;
 
-	rc = symlink_hash(link_len, link_str, md5_hash);
-	if (rc) {
-		cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
-		return rc;
-	}
+	md5(link_str, link_len, md5_hash);
 
 	scnprintf(md5_str2, sizeof(md5_str2),
 		  CIFS_MF_SYMLINK_MD5_FORMAT,
@@ -103,7 +83,6 @@ parse_mf_symlink(const u8 *buf, unsigned int buf_len, unsigned int *_link_len,
 static int
 format_mf_symlink(u8 *buf, unsigned int buf_len, const char *link_str)
 {
-	int rc;
 	unsigned int link_len;
 	unsigned int ofs;
 	u8 md5_hash[16];
@@ -116,11 +95,7 @@ format_mf_symlink(u8 *buf, unsigned int buf_len, const char *link_str)
 	if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)
 		return -ENAMETOOLONG;
 
-	rc = symlink_hash(link_len, link_str, md5_hash);
-	if (rc) {
-		cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
-		return rc;
-	}
+	md5(link_str, link_len, md5_hash);
 
 	scnprintf(buf, buf_len,
 		  CIFS_MF_SYMLINK_LEN_FORMAT CIFS_MF_SYMLINK_MD5_FORMAT,