linux-kernel - [ 24/85] target: fix NULL pointer dereference bug alloc

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Date:	Wed, 12 Sep 2012 16:36:07 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>, Yi Zou <yi.zou@...el.com>,
	Andy Grover <agrover@...hat.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	"Open-FCoE.org" <devel@...n-fcoe.org>
Subject: [ 24/85] target: fix NULL pointer dereference bug alloc_page() fails to get memory

From: Greg KH <gregkh@...uxfoundation.org>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yi Zou <yi.zou@...el.com>

commit d0e27c88d795fb9647153063ec48051fd84e1731 upstream.

I am hitting this bug when the target is low in memory that fails the
alloc_page() for the newly submitted command. This is a sort of off-by-one
bug causing NULL pointer dereference in __free_page() since 'i' here is
really the counter of total pages that have been successfully allocated here.

Signed-off-by: Yi Zou <yi.zou@...el.com>
Cc: Andy Grover <agrover@...hat.com>
Cc: Nicholas Bellinger <nab@...ux-iscsi.org>
Cc: Open-FCoE.org <devel@...n-fcoe.org>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/target/target_core_transport.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -3675,9 +3675,9 @@ transport_generic_get_mem(struct se_cmd
 	return 0;
 
 out:
-	while (i >= 0) {
-		__free_page(sg_page(&cmd->t_data_sg[i]));
+	while (i > 0) {
 		i--;
+		__free_page(sg_page(&cmd->t_data_sg[i]));
 	}
 	kfree(cmd->t_data_sg);
 	cmd->t_data_sg = NULL;


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