Fix bmp bug in ReadHeader()

For BmpMaskCodecs, we need to skip any offset after the
header to get to the start of pixel data.

Before this fix, we only skipped this data when codecOut
is non-NULL (instead of on every call to ReadHeader()).

https://gold.skia.org/search?q=1&neg=true&unt=false&query=name%3Drgb16-565pal.bmp_0.200%26name%3Drgb16-565pal.bmp%26name%3Drgb16-565pal.bmp_0.250%26name%3Drgb16-565pal.bmp_0.333%26name%3Drgb16-565pal.bmp_0.375%26name%3Drgb16-565pal.bmp_0.400%26name%3Drgb16-565pal.bmp_0.500%26source_type%3Dimage
BUG=skia:

Review URL: https://codereview.chromium.org/1318393004

1 files changed, 18 insertions, 14 deletions

diff --git a/src/codec/SkBmpCodec.cpp b/src/codec/SkBmpCodec.cpp
index 8d21e1dd8e..406a603dce 100644
--- a/src/codec/SkBmpCodec.cpp
+++ b/src/codec/SkBmpCodec.cpp
@@ -457,10 +457,23 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
     // Calculate the number of bytes read so far
     const uint32_t bytesRead = kBmpHeaderBytes + infoBytes + maskBytes;
     if (!inIco && offset < bytesRead) {
+        // TODO (msarett): Do we really want to fail if the offset in the header is invalid?
+        //                 Seems like we can just assume that the offset is zero and try to decode?
+        //                 Maybe we don't want to try to decode corrupt images?
         SkCodecPrintf("Error: pixel data offset less than header size.\n");
         return false;
     }
 
+    // Skip to the start of the pixel array.
+    // We can do this here because there is no color table to read
+    // in bit mask mode.
+    if (!inIco && kBitMask_BmpInputFormat == inputFormat) {
+        if (stream->skip(offset - bytesRead) != offset - bytesRead) {
+            SkCodecPrintf("Error: unable to skip to image data.\n");
+            return false;
+        }
+    }
+
     if (codecOut) {
         // Set the image info
         const SkImageInfo& imageInfo = SkImageInfo::Make(width, height,
@@ -469,9 +482,8 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
         // Return the codec
         switch (inputFormat) {
             case kStandard_BmpInputFormat:
-                *codecOut =
-                        new SkBmpStandardCodec(imageInfo, stream, bitsPerPixel, numColors,
-                                               bytesPerColor, offset - bytesRead, rowOrder, inIco);
+                *codecOut = new SkBmpStandardCodec(imageInfo, stream, bitsPerPixel, numColors,
+                        bytesPerColor, offset - bytesRead, rowOrder, inIco);
                 return true;
             case kBitMask_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
@@ -479,16 +491,9 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
                     SkCodecPrintf("Error: Icos may not use bit mask format.\n");
                     return false;
                 }
-                // Skip to the start of the pixel array.
-                // We can do this here because there is no color table to read
-                // in bit mask mode.
-                if (stream->skip(offset - bytesRead) != offset - bytesRead) {
-                    SkCodecPrintf("Error: unable to skip to image data.\n");
-                    return false;
-                }
 
                 *codecOut = new SkBmpMaskCodec(imageInfo, stream, bitsPerPixel, masks.detach(),
-                                               rowOrder);
+                        rowOrder);
                 return true;
             case kRLE_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
@@ -496,9 +501,8 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
                 // require that RLE Bmps have a valid number of totalBytes, and
                 // Icos skip the header that contains totalBytes.
                 SkASSERT(!inIco);
-                *codecOut =
-                        new SkBmpRLECodec(imageInfo, stream, bitsPerPixel, numColors, bytesPerColor,
-                                          offset - bytesRead, rowOrder, RLEBytes);
+                *codecOut = new SkBmpRLECodec(imageInfo, stream, bitsPerPixel, numColors,
+                        bytesPerColor, offset - bytesRead, rowOrder, RLEBytes);
                 return true;
             default:
                 SkASSERT(false);