[PATCH] register_console: prevent adding the same console twice

From: Andreas BieÃmann
Date: Fri Mar 22 2013 - 06:16:43 EST

This patch guards the console_drivers list to be corrupted. The
for_each_console() macro insist on a strictly forward list ended by NULL:


Without this patch it may happen easily to destroy this list for example by
adding 'earlyprintk' twice. This will result in the following list:


This in turn will result in an endless loop in console_unlock() later on by
printing the first __log_buf line endlessly.

Signed-off-by: Andreas BieÃmann <andreas@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Kay Sievers <kay@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
kernel/printk.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/kernel/printk.c b/kernel/printk.c
index 0b31715..f78bfcd 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -2254,6 +2254,14 @@ void register_console(struct console *newcon)
unsigned long flags;
struct console *bcon = NULL;

+ if (console_drivers)
+ for_each_console(bcon)
+ if (bcon == newcon) {
+ pr_warn("prevent adding console '%s%d' twice\n",
+ newcon->name, newcon->index);
+ return;
+ }
* before we register a new CON_BOOT console, make sure we don't
* already have a valid console

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