linux-kernel - [PATCH] Fix memory corruption in console selection

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Date:	Fri, 30 Jan 2009 15:27:14 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] Fix memory corruption in console selection

[ I don't know who is the console maintainer or if there is any, so I'm 
posting this to Linus ]


Fix an off-by-two memory error in console selection.

The loop below goes from sel_start to sel_end (inclusive), so it writes 
one more character. This one more character was added to the allocated 
size (+1), but it was not multiplied by an UTF-8 multiplier.

This patch fixes a memory corruption when UTF-8 console is used and the 
user selects a few characters, all of them 3-byte in UTF-8 (for example a 
frame line).

When memory redzones are enabled, a redzone corruption is reported. When 
they are not enabled, trashing of random memory occurs.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

---
 drivers/char/selection.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6.29-rc3-devel/drivers/char/selection.c
===================================================================
--- linux-2.6.29-rc3-devel.orig/drivers/char/selection.c	2009-01-30 21:03:07.000000000 +0100
+++ linux-2.6.29-rc3-devel/drivers/char/selection.c	2009-01-30 21:03:38.000000000 +0100
@@ -268,7 +268,7 @@ int set_selection(const struct tiocl_sel
 
 	/* Allocate a new buffer before freeing the old one ... */
 	multiplier = use_unicode ? 3 : 1;  /* chars can take up to 3 bytes */
-	bp = kmalloc((sel_end-sel_start)/2*multiplier+1, GFP_KERNEL);
+	bp = kmalloc(((sel_end-sel_start)/2+1)*multiplier, GFP_KERNEL);
 	if (!bp) {
 		printk(KERN_WARNING "selection: kmalloc() failed\n");
 		clear_selection();
--
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