[PATCH] efifb: prevent null dereferences by removing unused array indices from dmi_list

From: James Bates
Date: Tue Aug 06 2013 - 19:15:41 EST

Hi all,

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

Now efifb_setup(), L.322 & L.323, loops through all these array elements, and performs
a strcmp o a field (optname) in each item. For non explicitly initialized elements this
will be a null pointer:

for (i = 0; i < M_UNKNOWN; i++) {
if (!strcmp(this_opt, dmi_list[i].optname) &&

On my macbook6,1 the predefined values are for some reason incorrect, and most parameters
are preset correctly by my efi bootloader (elilo). but stride/line_length is not detected
correctly and so I wish to set it explicitly using a "video=efifb:stride:2048" command-line
argument. Because of the above null dereference, an exception (presumably) occurs before
the parsing code (L.333) is ever reached. I say presumably since the mac hangs on boot
without a console, and I can therefore not see any output.

By removing the unused values from the enum, and thus preventing implicitly initialized items
in the dmi_list array, the null dereference does not occur, my customer command-line arg is
parsed correctly, and my console displays correctly.

Signed-off-by: James Bates <james.h.bates@xxxxxxxxx>
drivers/video/efifb.c | 3 ---
1 file changed, 3 deletions(-)

diff --git a/drivers/video/efifb.c b/drivers/video/efifb.c
index 50fe668..52d1d88 100644
--- a/drivers/video/efifb.c
+++ b/drivers/video/efifb.c
@@ -50,12 +50,9 @@ enum {
M_MINI_3_1, /* Mac Mini, 3,1th gen */
M_MINI_4_1, /* Mac Mini, 4,1th gen */
M_MB, /* MacBook */
- M_MB_2, /* MacBook, 2nd rev. */
- M_MB_3, /* MacBook, 3rd rev. */
M_MB_5_1, /* MacBook, 5th rev. */
M_MB_6_1, /* MacBook, 6th rev. */
M_MB_7_1, /* MacBook, 7th rev. */
- M_MB_SR, /* MacBook, 2nd gen, (Santa Rosa) */
M_MBA, /* MacBook Air */
M_MBA_3, /* Macbook Air, 3rd rev */
M_MBP, /* MacBook Pro */
-- (Apple Git-37)

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