Merge tag 'printk-for-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

Pull printk updates from Petr Mladek:

 - Fix off-by-one error when calculating messages that might fit into
   kmsg buffer. It causes occasional omitting of the last message.

 - Add missing pointer check in %pD format modifier handling.

 - Some clean up

* tag 'printk-for-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
  ABI: Update dev-kmsg documentation to match current kernel behaviour
  printk: Replace strncmp() with str_has_prefix()
  lib/test_printf: Remove obvious comments from %pd and %pD tests
  lib/test_printf: Add test of null/invalid pointer dereference for dentry
  vsprintf: Prevent crash when dereferencing invalid pointers for %pD
  printk: Do not lose last line in kmsg buffer dump

kernel/printk/braille.c

@@ -11,11 +11,18 @@
 
 int _braille_console_setup(char **str, char **brl_options)
 {
-	if (!strncmp(*str, "brl,", 4)) {
+	size_t len;
+
+	len = str_has_prefix(*str, "brl,");
+	if (len) {
 		*brl_options = "";
-		*str += 4;
-	} else if (!strncmp(*str, "brl=", 4)) {
-		*brl_options = *str + 4;
+		*str += len;
+		return 0;
+	}
+
+	len = str_has_prefix(*str, "brl=");
+	if (len) {
+		*brl_options = *str + len;
 		*str = strchr(*brl_options, ',');
 		if (!*str) {
 			pr_err("need port name after brl=\n");

kernel/printk/printk.c

@@ -118,19 +118,29 @@ static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
 
 static int __control_devkmsg(char *str)
 {
+	size_t len;
+
 	if (!str)
 		return -EINVAL;
 
-	if (!strncmp(str, "on", 2)) {
+	len = str_has_prefix(str, "on");
+	if (len) {
 		devkmsg_log = DEVKMSG_LOG_MASK_ON;
-		return 2;
-	} else if (!strncmp(str, "off", 3)) {
-		devkmsg_log = DEVKMSG_LOG_MASK_OFF;
-		return 3;
-	} else if (!strncmp(str, "ratelimit", 9)) {
-		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
-		return 9;
+		return len;
 	}
+
+	len = str_has_prefix(str, "off");
+	if (len) {
+		devkmsg_log = DEVKMSG_LOG_MASK_OFF;
+		return len;
+	}
+
+	len = str_has_prefix(str, "ratelimit");
+	if (len) {
+		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
+		return len;
+	}
+
 	return -EINVAL;
 }
 
@@ -3274,7 +3284,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	/* move first record forward until length fits into the buffer */
 	seq = dumper->cur_seq;
 	idx = dumper->cur_idx;
-	while (l > size && seq < dumper->next_seq) {
+	while (l >= size && seq < dumper->next_seq) {
 		struct printk_log *msg = log_from_idx(idx);
 
 		l -= msg_print_text(msg, true, time, NULL, 0);