[PATCH] printk: fix return value of printk.devkmsg __setup handler

* [PATCH] printk: fix return value of printk.devkmsg __setup handler
@ 2022-02-28 22:05 Randy Dunlap
  2022-03-01 12:58 ` John Ogness
                   ` (3 more replies)
  0 siblings, 4 replies; 6+ messages in thread
From: Randy Dunlap @ 2022-02-28 22:05 UTC (permalink / raw)
  To: linux-kernel
  Cc: Randy Dunlap, Igor Zhbanov, Borislav Petkov, Andrew Morton,
	Petr Mladek, Sergey Senozhatsky, Steven Rostedt, John Ogness

If an invalid option value is used with "printk.devkmsg=<value>",
it is silently ignored.
If a valid option value is used, it is honored but the wrong return
value (0) is used, indicating that the command line option had an
error and was not handled. This string is not added to init's
environment strings due to init/main.c::unknown_bootoption()
checking for a '.' in the boot option string and then considering
that string to be an "Unused module parameter".

Print a warning message if a bad option string is used.
Always return 1 from the __setup handler to indicate that the command
line option has been handled.

Fixes: 750afe7babd1 ("printk: add kernel parameter to control writes to /dev/kmsg")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Cc: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
---
 kernel/printk/printk.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- linux-next-20220228.orig/kernel/printk/printk.c
+++ linux-next-20220228/kernel/printk/printk.c
@@ -152,8 +152,10 @@ static int __control_devkmsg(char *str)
 
 static int __init control_devkmsg(char *str)
 {
-	if (__control_devkmsg(str) < 0)
+	if (__control_devkmsg(str) < 0) {
+		pr_warn("printk.devkmsg: bad option string '%s'\n", str);
 		return 1;
+	}
 
 	/*
 	 * Set sysctl string accordingly:
@@ -172,7 +174,7 @@ static int __init control_devkmsg(char *
 	 */
 	devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
 
-	return 0;
+	return 1;
 }
 __setup("printk.devkmsg=", control_devkmsg);
 

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