linux-kernel - [PATCH v2] efifb: prevent null-deref when iterating dmi

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Message-Id: <1380732056-5387-1-git-send-email-dh.herrmann@gmail.com>
Date:	Wed,  2 Oct 2013 18:40:56 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	linux-fbdev@...r.kernel.org
Cc:	James Bates <james.h.bates@...il.com>,
	linux-kernel@...r.kernel.org,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	David Herrmann <dh.herrmann@...il.com>,
	James Bates <james.h.bates@...oo.com>
Subject: [PATCH v2] efifb: prevent null-deref when iterating dmi_list

The dmi_list array is initialized using gnu designated initializers, and
therefore may contain fewer explicitly defined entries as there are
elements in it. This is because the enum above with M_xyz constants
contains more items than the designated initializer. Those elements not
explicitly initialized are implicitly set to 0.

Now efifb_setup() loops through all these array elements, and performs
a strcmp on each item. For non explicitly initialized elements this will
be a null pointer:

This patch swaps the check order in the if statement, thus checks first
whether dmi_list[i].base is null.

Signed-off-by: James Bates <james.h.bates@...oo.com>
Signed-off-by: David Herrmann <dh.herrmann@...il.com>
---
Hi

As James didn't respond to the last emails, I just rebased the patch and resent
it. The efi M_xyz constants were moved to x86-sysfb so if anyone wants to remove
unused bits, please send a separate patch to LKML and x86-ML. This patch just
fixes the NULL-deref.

Thanks
David

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

diff --git a/drivers/video/efifb.c b/drivers/video/efifb.c
index 7f9ff75..fcb9500 100644
--- a/drivers/video/efifb.c
+++ b/drivers/video/efifb.c
@@ -108,8 +108,8 @@ static int efifb_setup(char *options)
 			if (!*this_opt) continue;

 			for (i = 0; i < M_UNKNOWN; i++) {
-				if (!strcmp(this_opt, efifb_dmi_list[i].optname) &&
-				    efifb_dmi_list[i].base != 0) {
+				if (efifb_dmi_list[i].base != 0 &&
+				    !strcmp(this_opt, efifb_dmi_list[i].optname)) {
 					screen_info.lfb_base = efifb_dmi_list[i].base;
 					screen_info.lfb_linelength = efifb_dmi_list[i].stride;
 					screen_info.lfb_width = efifb_dmi_list[i].width;
-- 
1.8.4

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