[PATCH] init: Carefuly handle loglevel option passed to kernel cmdline.

[PATCH] init: Carefuly handle loglevel option passed to kernel cmdline.

[Alexander Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@sysgo.com>

Carefuly handle loglevel option passed to kernel cmdline.

When malformed loglevel value (for example "${abc}") passed to kernel
cmdline, the loglevel itself is being set to 0. This suppresses all
following messages, including all the errors and crashes caused by
other malformed cmdline options. This could make debugging process
quite tricky. Provided modifications leaves previous value of loglevel
if the new value is incorrect and report error code in this case.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@sysgo.com>
---
--- linux.old/init/main.c	2011-09-20 15:23:05.038279428 +0200
+++ linux/init/main.c	2011-09-20 15:23:44.064930478 +0200
@@ -209,7 +209,18 @@ early_param("quiet", quiet_kernel);
 
 static int __init loglevel(char *str)
 {
-	get_option(&str, &console_loglevel);
+	int tmp_loglevel;
+
+	/*
+	 * Only update loglevel value when correct setting was passed,
+	 * to prevent blind crashes (when loglevel being set to 0) that
+	 * are quite hard to debug
+	 */
+	if (get_option(&str, &tmp_loglevel))
+		console_loglevel = tmp_loglevel;
+	else
+		return EINVAL;
+
 	return 0;
 }
 

Re: [PATCH] init: Carefuly handle loglevel option passed to kernel cmdline.

[Linus Torvalds]

On Tue, Sep 20, 2011 at 6:45 AM, Alexander Sverdlin <asv@sysgo.com> wrote:
>
> Carefuly handle loglevel option passed to kernel cmdline.

Ugh. I dislike how you misuse the error numbers - it *happens* to
work, but we return negative error numbers, not positive ones in the
kernel.

Also, doing an if/else when one arm does a return just looks overly complicated.

Does this (whitespace-damaged) patch work for you?

                 Linus

---
 init/main.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/init/main.c b/init/main.c
index 9c51ee7adf3d..5827722ec491 100644
--- a/init/main.c
+++ b/init/main.c
@@ -209,7 +209,11 @@ early_param("quiet", quiet_kernel);

 static int __init loglevel(char *str)
 {
-       get_option(&str, &console_loglevel);
+       int loglevel;
+
+       if (!get_option(&str, &loglevel))
+               return -EINVAL;
+       console_loglevel = loglevel;
        return 0;
 }

[PATCH] init: Carefuly handle loglevel option passed to kernel cmdline

[Alexander Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@sysgo.com>

Carefuly handle loglevel option passed to kernel cmdline.

When malformed loglevel value (for example "${abc}") passed to kernel
cmdline, the loglevel itself is being set to 0. This suppresses all
following messages, including all the errors and crashes caused by
other malformed cmdline options. This could make debugging process
quite tricky. Provided modifications leaves previous value of loglevel
if the new value is incorrect and report error code in this case.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@sysgo.com>
---
--- linux.old/init/main.c	2011-09-20 15:23:05.038279428 +0200
+++ linux/init/main.c	2011-09-21 09:39:24.266516051 +0200
@@ -209,8 +209,19 @@ early_param("quiet", quiet_kernel);
 
 static int __init loglevel(char *str)
 {
-	get_option(&str, &console_loglevel);
-	return 0;
+	int tmp_loglevel;
+
+	/*
+	 * Only update loglevel value when correct setting was passed,
+	 * to prevent blind crashes (when loglevel being set to 0) that
+	 * are quite hard to debug
+	 */
+	if (get_option(&str, &tmp_loglevel)) {
+		console_loglevel = tmp_loglevel;
+		return 0;
+	}
+
+	return -EINVAL;
 }
 
 early_param("loglevel", loglevel);