kdb: Eliminate strncpy() warnings by replacing with strscpy()

Currently the code to manage the kdb history buffer uses strncpy() to
copy strings to/and from the history and exhibits the classic "but
nobody ever told me that strncpy() doesn't always terminate strings"
bug. Modern gcc compilers recognise this bug and issue a warning.

In reality these calls will only abridge the copied string if kdb_read()
has *already* overflowed the command buffer. Thus the use of counted
copies here is only used to reduce the secondary effects of a bug
elsewhere in the code.

Therefore transitioning these calls into strscpy() (without checking
the return code) is appropriate.

Signed-off-by: Daniel Thompson <[email protected]>
Reviewed-by: Douglas Anderson <[email protected]>

kernel/debug/kdb/kdb_main.c

@@ -1102,12 +1102,12 @@ static int handle_ctrl_cmd(char *cmd)
 	case CTRL_P:
 		if (cmdptr != cmd_tail)
 			cmdptr = (cmdptr-1) % KDB_CMD_HISTORY_COUNT;
-		strncpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
+		strscpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
 		return 1;
 	case CTRL_N:
 		if (cmdptr != cmd_head)
 			cmdptr = (cmdptr+1) % KDB_CMD_HISTORY_COUNT;
-		strncpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
+		strscpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
 		return 1;
 	}
 	return 0;
@@ -1314,7 +1314,7 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
 		if (*cmdbuf != '\n') {
 			if (*cmdbuf < 32) {
 				if (cmdptr == cmd_head) {
-					strncpy(cmd_hist[cmd_head], cmd_cur,
+					strscpy(cmd_hist[cmd_head], cmd_cur,
 						CMD_BUFLEN);
 					*(cmd_hist[cmd_head] +
 					  strlen(cmd_hist[cmd_head])-1) = '\0';
@@ -1324,7 +1324,7 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
 				cmdbuf = cmd_cur;
 				goto do_full_getstr;
 			} else {
-				strncpy(cmd_hist[cmd_head], cmd_cur,
+				strscpy(cmd_hist[cmd_head], cmd_cur,
 					CMD_BUFLEN);
 			}