[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 <redacted>
Signed-off-by: David Herrmann <redacted>
---
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

From: James Bates <redacted>

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 <redacted>
Signed-off-by: David Herrmann <redacted>
---
v3: fixes the "Author" field and James' email address

 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

ping

On Wed, Oct 2, 2013 at 6:43 PM, David Herrmann [off-list ref] wrote:

On 02/10/13 19:43, David Herrmann wrote:

Thanks, queued for 3.13.

 Tomi

On 18:40 Wed 02 Oct     , David Herrmann wrote:

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 <redacted>
Signed-off-by: David Herrmann <redacted>

with the simpleDRM arriving next merge I'm wondering if we need to keep it?

Best Regaards,
J.

Hi

On Thu, Oct 31, 2013 at 11:45 AM, Jean-Christophe PLAGNIOL-VILLARD
[off-list ref] wrote:

On 18:40 Wed 02 Oct     , David Herrmann wrote:

quoted

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 <redacted>
Signed-off-by: David Herrmann <redacted>

with the simpleDRM arriving next merge I'm wondering if we need to keep it?

SimpleDRM is not coming next merge-window. It's basically finished,
but I'm still working on the user-space side as its KMS api is highly
reduced compared to fully-featured DRM/KMS drivers. Maybe 3.13 will
work out.

Anyhow, this patch is still needed as it fixes a serious bug for simplefb.

Thanks
David

On 17:17 Thu 31 Oct     , David Herrmann wrote:

Hi

On Thu, Oct 31, 2013 at 11:45 AM, Jean-Christophe PLAGNIOL-VILLARD
[off-list ref] wrote:

quoted

On 18:40 Wed 02 Oct     , David Herrmann wrote:

quoted

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 <redacted>
Signed-off-by: David Herrmann <redacted>

with the simpleDRM arriving next merge I'm wondering if we need to keep it?

SimpleDRM is not coming next merge-window. It's basically finished,
but I'm still working on the user-space side as its KMS api is highly
reduced compared to fully-featured DRM/KMS drivers. Maybe 3.13 will
work out.

do you have a git tree for the simpleDRM that I can pull?

Anyhow, this patch is still needed as it fixes a serious bug for simplefb.

ok

Thanks
David

Hi

On Fri, Nov 1, 2013 at 12:10 PM, Jean-Christophe PLAGNIOL-VILLARD
[off-list ref] wrote:

On 17:17 Thu 31 Oct     , David Herrmann wrote:

quoted

Hi

On Thu, Oct 31, 2013 at 11:45 AM, Jean-Christophe PLAGNIOL-VILLARD
[off-list ref] wrote:

quoted

On 18:40 Wed 02 Oct     , David Herrmann wrote:

quoted

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 <redacted>
Signed-off-by: David Herrmann <redacted>

with the simpleDRM arriving next merge I'm wondering if we need to keep it?

SimpleDRM is not coming next merge-window. It's basically finished,
but I'm still working on the user-space side as its KMS api is highly
reduced compared to fully-featured DRM/KMS drivers. Maybe 3.13 will
work out.

do you have a git tree for the simpleDRM that I can pull?

Sure, I usually push it to my fdo tree:
  http://cgit.freedesktop.org/~dvdhrm/linux/log/?h=simpledrm
But note that you shouldn't be using it right now. User-space fails on
it as SimpleDRM only provides a single KMS-FB. It also needs to be
adjusted to the new x86-sysfb changes and I am reworking the handover
to real drivers.

Cheers
David