um: Remove strlcpy declaration

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().
No return values were used, so direct replacement is safe.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230703160641.1790935-1-azeemshaikh38@gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>

arch/um/include/shared/user.h

@@ -50,7 +50,6 @@ static inline int printk(const char *fmt, ...)
 #endif
 
 extern int in_aton(char *str);
-extern size_t strlcpy(char *, const char *, size_t);
 extern size_t strlcat(char *, const char *, size_t);
 extern size_t strscpy(char *, const char *, size_t);
 

arch/um/os-Linux/umid.c

@@ -40,7 +40,7 @@ static int __init make_uml_dir(void)
 				__func__);
 			goto err;
 		}
-		strlcpy(dir, home, sizeof(dir));
+		strscpy(dir, home, sizeof(dir));
 		uml_dir++;
 	}
 	strlcat(dir, uml_dir, sizeof(dir));
@@ -243,7 +243,7 @@ int __init set_umid(char *name)
 	if (strlen(name) > UMID_LEN - 1)
 		return -E2BIG;
 
-	strlcpy(umid, name, sizeof(umid));
+	strscpy(umid, name, sizeof(umid));
 
 	return 0;
 }
@@ -262,7 +262,7 @@ static int __init make_umid(void)
 	make_uml_dir();
 
 	if (*umid == '\0') {
-		strlcpy(tmp, uml_dir, sizeof(tmp));
+		strscpy(tmp, uml_dir, sizeof(tmp));
 		strlcat(tmp, "XXXXXX", sizeof(tmp));
 		fd = mkstemp(tmp);
 		if (fd < 0) {