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

Documentation/ABI/testing/dev-kmsg

@@ -12,7 +12,7 @@ Description:	The /dev/kmsg character device node provides userspace access
 		The logged line can be prefixed with a <N> syslog prefix, which
 		carries the syslog priority and facility. The single decimal
 		prefix number is composed of the 3 lowest bits being the syslog
-		priority and the higher bits the syslog facility number.
+		priority and the next 8 bits the syslog facility number.
 
 		If no prefix is given, the priority number is the default kernel
 		log priority and the facility number is set to LOG_USER (1). It
@@ -90,13 +90,12 @@ Description:	The /dev/kmsg character device node provides userspace access
 		  +sound:card0 - subsystem:devname
 
 		The flags field carries '-' by default. A 'c' indicates a
-		fragment of a line. All following fragments are flagged with
-		'+'. Note, that these hints about continuation lines are not
-		necessarily correct, and the stream could be interleaved with
-		unrelated messages, but merging the lines in the output
-		usually produces better human readable results. A similar
-		logic is used internally when messages are printed to the
-		console, /proc/kmsg or the syslog() syscall.
+		fragment of a line. Note, that these hints about continuation
+		lines are not necessarily correct, and the stream could be
+		interleaved with unrelated messages, but merging the lines in
+		the output usually produces better human readable results. A
+		similar logic is used internally when messages are printed to
+		the console, /proc/kmsg or the syslog() syscall.
 
 		By default, kernel tries to avoid fragments by concatenating
 		when it can and fragments are rare; however, when extended

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)) {
+		return len;
+	}
+
+	len = str_has_prefix(str, "off");
+	if (len) {
 		devkmsg_log = DEVKMSG_LOG_MASK_OFF;
-		return 3;
-	} else if (!strncmp(str, "ratelimit", 9)) {
+		return len;
+	}
+
+	len = str_has_prefix(str, "ratelimit");
+	if (len) {
 		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
-		return 9;
+		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);

lib/test_printf.c

@@ -455,6 +455,11 @@ dentry(void)
 	test("foo", "%pd", &test_dentry[0]);
 	test("foo", "%pd2", &test_dentry[0]);
 
+	test("(null)", "%pd", NULL);
+	test("(efault)", "%pd", PTR_INVALID);
+	test("(null)", "%pD", NULL);
+	test("(efault)", "%pD", PTR_INVALID);
+
 	test("romeo", "%pd", &test_dentry[3]);
 	test("alfa/romeo", "%pd2", &test_dentry[3]);
 	test("bravo/alfa/romeo", "%pd3", &test_dentry[3]);

lib/vsprintf.c

@@ -869,6 +869,15 @@ char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_sp
 	return widen_string(buf, n, end, spec);
 }
 
+static noinline_for_stack
+char *file_dentry_name(char *buf, char *end, const struct file *f,
+			struct printf_spec spec, const char *fmt)
+{
+	if (check_pointer(&buf, end, f, spec))
+		return buf;
+
+	return dentry_name(buf, end, f->f_path.dentry, spec, fmt);
+}
 #ifdef CONFIG_BLOCK
 static noinline_for_stack
 char *bdev_name(char *buf, char *end, struct block_device *bdev,
@@ -2166,9 +2175,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	case 'C':
 		return clock(buf, end, ptr, spec, fmt);
 	case 'D':
-		return dentry_name(buf, end,
-				   ((const struct file *)ptr)->f_path.dentry,
-				   spec, fmt);
+		return file_dentry_name(buf, end, ptr, spec, fmt);
 #ifdef CONFIG_BLOCK
 	case 'g':
 		return bdev_name(buf, end, ptr, spec, fmt);