linux-kernel - [PATCH] video: fbdev: sis: fix null ptr dereference

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Date:   Wed,  5 Aug 2020 07:52:08 -0700
From:   trix@...hat.com
To:     thomas@...ischhofer.net, b.zolnierkie@...sung.com, akpm@...l.org
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tom Rix <trix@...hat.com>
Subject: [PATCH] video: fbdev: sis: fix null ptr dereference

From: Tom Rix <trix@...hat.com>

Clang static analysis reports this representative error

init.c:2501:18: warning: Array access (from variable 'queuedata') results
  in a null pointer dereference
      templ |= ((queuedata[i] & 0xc0) << 3);

This is the problem block of code

   if(ModeNo > 0x13) {
      ...
      if(SiS_Pr->ChipType == SIS_730) {
	 queuedata = &FQBQData730[0];
      } else {
	 queuedata = &FQBQData[0];
      }
   } else {

   }

queuedata is not set in the else block

Reviewing the old code, the arrays FQBQData730 and FQBQData were
used directly.

So hoist the setting of queuedata out of the if-else block.

Fixes: 544393fe584d ("[PATCH] sisfb update")

Signed-off-by: Tom Rix <trix@...hat.com>
---
 drivers/video/fbdev/sis/init.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/video/fbdev/sis/init.c b/drivers/video/fbdev/sis/init.c
index dfe3eb769638..fde27feae5d0 100644
--- a/drivers/video/fbdev/sis/init.c
+++ b/drivers/video/fbdev/sis/init.c
@@ -2428,6 +2428,11 @@ SiS_SetCRT1FIFO_630(struct SiS_Private *SiS_Pr, unsigned short ModeNo,
 
    i = 0;
 
+	if (SiS_Pr->ChipType == SIS_730)
+		queuedata = &FQBQData730[0];
+	else
+		queuedata = &FQBQData[0];
+
    if(ModeNo > 0x13) {
 
       /* Get VCLK  */
@@ -2445,12 +2450,6 @@ SiS_SetCRT1FIFO_630(struct SiS_Private *SiS_Pr, unsigned short ModeNo,
       /* Get half colordepth */
       colorth = colortharray[(SiS_Pr->SiS_ModeType - ModeEGA)];
 
-      if(SiS_Pr->ChipType == SIS_730) {
-	 queuedata = &FQBQData730[0];
-      } else {
-	 queuedata = &FQBQData[0];
-      }
-
       do {
 	 templ = SiS_CalcDelay2(SiS_Pr, queuedata[i]) * VCLK * colorth;
 
-- 
2.18.1