kdb: Replace deprecated strcpy() with memmove() in vkdb_printf()

strcpy() is deprecated and its behavior is undefined when the source and
destination buffers overlap. Use memmove() instead to avoid any
undefined behavior.

Adjust comments for clarity.

Link: KSPP#88
Fixes: 5d5314d ("kdb: core for kgdb back end (1 of 2)")
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Daniel Thompson (RISCstar) <danielt@kernel.org>

Author: toblux

kernel/debug/kdb/kdb_io.c

@@ -714,8 +714,8 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 		 * it, depending on the results of the search.
 		 */
 		cp++;	 	     /* to byte after the newline */
-		replaced_byte = *cp; /* remember what/where it was */
-		cphold = cp;
+		replaced_byte = *cp; /* remember what it was */
+		cphold = cp;	     /* remember where it was */
 		*cp = '\0';	     /* end the string for our search */
 
 		/*
@@ -732,8 +732,9 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 			 * Shift the buffer left.
 			 */
 			*cphold = replaced_byte;
-			strcpy(kdb_buffer, cphold);
-			len = strlen(kdb_buffer);
+			len = strlen(cphold);
+			/* Use memmove() because the buffers overlap */
+			memmove(kdb_buffer, cphold, len + 1);
 			next_avail = kdb_buffer + len;
 			size_avail = sizeof(kdb_buffer) - len;
 			goto kdb_print_out;
@@ -872,8 +873,9 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 	 */
 	if (kdb_grepping_flag && !suspend_grep) {
 		*cphold = replaced_byte;
-		strcpy(kdb_buffer, cphold);
-		len = strlen(kdb_buffer);
+		len = strlen(cphold);
+		/* Use memmove() because the buffers overlap */
+		memmove(kdb_buffer, cphold, len + 1);
 		next_avail = kdb_buffer + len;
 		size_avail = sizeof(kdb_buffer) - len;
 	}