[PATCH] register_console: prevent adding the same console twice

[Andreas BieÃmann]

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

 con0->next->con1->next->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:

 con0->next->con0

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
-- 
1.7.10.4

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