strmove(): Add API, and use it instead of its pattern

lib/Makefile.am

@@ -115,6 +115,8 @@ libshadow_la_SOURCES = \
 	lockpw.c \
 	loginprompt.c \
 	mail.c \
+	memory/memcpy/memmove.c \
+	memory/memcpy/memmove.h \
 	motd.c \
 	myname.c \
 	nss.c \
@@ -223,6 +225,8 @@ libshadow_la_SOURCES = \
 	string/strcmp/strprefix.h \
 	string/strcpy/stpecpy.c \
 	string/strcpy/stpecpy.h \
+	string/strcpy/strmove.c \
+	string/strcpy/strmove.h \
 	string/strcpy/strncat.c \
 	string/strcpy/strncat.h \
 	string/strcpy/strncpy.c \

lib/memory/memcpy/memmove.c

@@ -0,0 +1,7 @@
+// SPDX-FileCopyrightText: 2025-2026, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#include "config.h"
+
+#include "memory/memcpy/memmove.h"

lib/memory/memcpy/memmove.h

@@ -0,0 +1,26 @@
+// SPDX-FileCopyrightText: 2025-2026, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#ifndef SHADOW_INCLUDE_LIB_MEMORY_MEMCPY_MEMMOVE_H_
+#define SHADOW_INCLUDE_LIB_MEMORY_MEMCPY_MEMMOVE_H_
+
+
+#include "config.h"
+
+#include <memory.h>
+
+#include "sizeof.h"
+
+
+// memmove_T - memory move type-safe
+#define memmove_T(dst, src, n, T)   memmove_T_(dst, src, n, typeas(T))
+#define memmove_T_(dst, src, n, T)  do                                \
+{                                                                     \
+	_Generic(dst, T *: (void)0);                                  \
+	_Generic(src, T *: (void)0);                                  \
+	memmove(dst, src, (n) * sizeof(T));                           \
+} while (0)
+
+
+#endif  // include guard

lib/string/README

@@ -186,6 +186,10 @@ strcpy/ - String copying
 	Do NOT use.  I'll remove it soon.
 
   s/
+    strmove()
+	Like memmove(3), for strings.  It takes the length of the string
+	internally with strlen(3).
+
     strtcpy()
 	Copy from a string into another string with truncation.
 	This is what the Linux kernel calls strscpy().
@@ -208,6 +212,9 @@ strcpy/ - String copying
     MEMCPY()
 	Like memcpy(3), but takes two arrays.
 
+    memmove_T()
+	Like memmove(3), but type safe.
+
 sprintf/ - Formatted string creation
 
     aprintf(3)

lib/string/strcpy/strmove.c

@@ -0,0 +1,10 @@
+// SPDX-FileCopyrightText: 2025-2026, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#include "config.h"
+
+#include "string/strcpy/strmove.h"
+
+
+extern inline void strmove(char *dst, char *src);

lib/string/strcpy/strmove.h

@@ -0,0 +1,29 @@
+// SPDX-FileCopyrightText: 2025-2026, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#ifndef SHADOW_INCLUDE_LIB_STRING_STRCPY_STRMOVE_H_
+#define SHADOW_INCLUDE_LIB_STRING_STRCPY_STRMOVE_H_
+
+
+#include "config.h"
+
+#include <string.h>
+
+#include "attr.h"
+#include "memory/memcpy/memmove.h"
+
+
+ATTR_STRING(2)
+inline void strmove(char *dst, char *src);
+
+
+// strmove - string move
+inline void
+strmove(char *dst, char *src)
+{
+	memmove_T(dst, src, strlen(src) + 1, char);
+}
+
+
+#endif  // include guard

src/usermod.c

@@ -65,6 +65,7 @@
 #include "string/sprintf/aprintf.h"
 #include "string/strcmp/streq.h"
 #include "string/strcmp/strprefix.h"
+#include "string/strcpy/strmove.h"
 #include "string/strdup/strdup.h"
 #include "string/strspn/stprspn.h"
 #include "sysconf.h"
@@ -489,7 +490,7 @@ new_pw_passwd(char *pw_pass, bool process_selinux)
 		              "updating-password", user_newname, user_newid, 1);
 #endif
 		SYSLOG(LOG_INFO, "unlock user '%s' password", user_newname);
-		memmove(pw_pass, pw_pass + 1, strlen(pw_pass));
+		strmove(pw_pass, pw_pass + 1);
 	} else if (pflg) {
 #ifdef WITH_AUDIT
 		audit_logger (AUDIT_USER_CHAUTHTOK,