kdb: Use strscpy with destination buffer size

gcc 8.1.0 warns with:

kernel/debug/kdb/kdb_support.c: In function ‘kallsyms_symbol_next’:
kernel/debug/kdb/kdb_support.c:239:4: warning: ‘strncpy’ specified bound depends on the length of the source argument [-Wstringop-overflow=]
     strncpy(prefix_name, name, strlen(name)+1);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
kernel/debug/kdb/kdb_support.c:239:31: note: length computed here

Use strscpy() with the destination buffer size, and use ellipses when
displaying truncated symbols.

v2: Use strscpy()
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Jonathan Toppins <jtoppins@redhat.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: kgdb-bugreport@lists.sourceforge.net
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

kernel/debug/kdb/kdb_io.c

@@ -216,7 +216,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
 	int count;
 	int i;
 	int diag, dtab_count;
-	int key;
+	int key, buf_size, ret;
 
 
 	diag = kdbgetintenv("DTABCOUNT", &dtab_count);
@@ -336,9 +336,8 @@ static char *kdb_read(char *buffer, size_t bufsize)
 		else
 			p_tmp = tmpbuffer;
 		len = strlen(p_tmp);
-		count = kallsyms_symbol_complete(p_tmp,
-						 sizeof(tmpbuffer) -
-						 (p_tmp - tmpbuffer));
+		buf_size = sizeof(tmpbuffer) - (p_tmp - tmpbuffer);
+		count = kallsyms_symbol_complete(p_tmp, buf_size);
 		if (tab == 2 && count > 0) {
 			kdb_printf("\n%d symbols are found.", count);
 			if (count > dtab_count) {
@@ -350,9 +349,13 @@ static char *kdb_read(char *buffer, size_t bufsize)
 			}
 			kdb_printf("\n");
 			for (i = 0; i < count; i++) {
-				if (WARN_ON(!kallsyms_symbol_next(p_tmp, i)))
+				ret = kallsyms_symbol_next(p_tmp, i, buf_size);
+				if (WARN_ON(!ret))
 					break;
-				kdb_printf("%s ", p_tmp);
+				if (ret != -E2BIG)
+					kdb_printf("%s ", p_tmp);
+				else
+					kdb_printf("%s... ", p_tmp);
 				*(p_tmp + len) = '\0';
 			}
 			if (i >= dtab_count)

kernel/debug/kdb/kdb_private.h

@@ -83,7 +83,7 @@ typedef struct __ksymtab {
 		unsigned long sym_start;
 		unsigned long sym_end;
 		} kdb_symtab_t;
-extern int kallsyms_symbol_next(char *prefix_name, int flag);
+extern int kallsyms_symbol_next(char *prefix_name, int flag, int buf_size);
 extern int kallsyms_symbol_complete(char *prefix_name, int max_len);
 
 /* Exported Symbols for kernel loadable modules to use. */

kernel/debug/kdb/kdb_support.c

@@ -221,11 +221,13 @@ int kallsyms_symbol_complete(char *prefix_name, int max_len)
  * Parameters:
  *	prefix_name	prefix of a symbol name to lookup
  *	flag	0 means search from the head, 1 means continue search.
+ *	buf_size	maximum length that can be written to prefix_name
+ *			buffer
  * Returns:
  *	1 if a symbol matches the given prefix.
  *	0 if no string found
  */
-int kallsyms_symbol_next(char *prefix_name, int flag)
+int kallsyms_symbol_next(char *prefix_name, int flag, int buf_size)
 {
 	int prefix_len = strlen(prefix_name);
 	static loff_t pos;
@@ -235,10 +237,8 @@ int kallsyms_symbol_next(char *prefix_name, int flag)
 		pos = 0;
 
 	while ((name = kdb_walk_kallsyms(&pos))) {
-		if (strncmp(name, prefix_name, prefix_len) == 0) {
-			strncpy(prefix_name, name, strlen(name)+1);
-			return 1;
-		}
+		if (!strncmp(name, prefix_name, prefix_len))
+			return strscpy(prefix_name, name, buf_size);
 	}
 	return 0;
 }