From cc50d843089c8cf386c3e0f9cb2fae0b258a9b7b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
Date: Mon, 18 Feb 2019 13:53:16 +0100
Subject: [PATCH] CVE-2019-7637: Fix in integer overflow in SDL_CalculatePitch
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If a too large width is passed to SDL_SetVideoMode() the width travels
to SDL_CalculatePitch() where the width (e.g. 65535) is multiplied by
BytesPerPixel (e.g. 4) and the result is stored into Uint16 pitch
variable. During this arithmetics an integer overflow can happen (e.g.
the value is clamped as 65532). As a result SDL_Surface with a pitch
smaller than width * BytesPerPixel is created, too small pixel buffer
is allocated and when the SDL_Surface is processed in SDL_FillRect()
a buffer overflow occurs.

This can be reproduced with "./graywin -width 21312312313123213213213"
command.

This patch fixes is by using a very careful arithmetics in
SDL_CalculatePitch(). If an overflow is detected, an error is reported
back as a special 0 value. We assume that 0-width surfaces do not
occur in the wild. Since SDL_CalculatePitch() is a private function,
we can change the semantics.

CVE-2019-7637
https://bugzilla.libsdl.org/show_bug.cgi?id=4497

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 src/video/SDL_pixels.c          | 41 +++++++++++++++++++++++++++------
 src/video/gapi/SDL_gapivideo.c  |  3 +++
 src/video/nanox/SDL_nxvideo.c   |  4 ++++
 src/video/ps2gs/SDL_gsvideo.c   |  3 +++
 src/video/ps3/SDL_ps3video.c    |  3 +++
 src/video/windib/SDL_dibvideo.c |  3 +++
 src/video/windx5/SDL_dx5video.c |  3 +++
 src/video/x11/SDL_x11video.c    |  4 ++++
 8 files changed, 57 insertions(+), 7 deletions(-)

diff --git a/src/video/SDL_pixels.c b/src/video/SDL_pixels.c
index 1a7fd51..44626b7 100644
--- a/src/video/SDL_pixels.c
+++ b/src/video/SDL_pixels.c
@@ -286,26 +286,53 @@ void SDL_DitherColors(SDL_Color *colors, int bpp)
 	}
 }
 /* 
- * Calculate the pad-aligned scanline width of a surface
+ * Calculate the pad-aligned scanline width of a surface. Return 0 in case of
+ * an error.
  */
 Uint16 SDL_CalculatePitch(SDL_Surface *surface)
 {
-	Uint16 pitch;
+	unsigned int pitch = 0;
 
 	/* Surface should be 4-byte aligned for speed */
-	pitch = surface->w*surface->format->BytesPerPixel;
+	/* The code tries to prevent from an Uint16 overflow. */;
+	for (Uint8 byte = surface->format->BytesPerPixel; byte; byte--) {
+		pitch += (unsigned int)surface->w;
+		if (pitch < surface->w) {
+			SDL_SetError("A scanline is too wide");
+			return(0);
+		}
+	}
 	switch (surface->format->BitsPerPixel) {
 		case 1:
-			pitch = (pitch+7)/8;
+			if (pitch % 8) {
+				pitch = pitch / 8 + 1;
+			} else {
+				pitch = pitch / 8;
+			}
 			break;
 		case 4:
-			pitch = (pitch+1)/2;
+			if (pitch % 2) {
+				pitch = pitch / 2 + 1;
+			} else {
+				pitch = pitch / 2;
+			}
 			break;
 		default:
 			break;
 	}
-	pitch = (pitch + 3) & ~3;	/* 4-byte aligning */
-	return(pitch);
+	/* 4-byte aligning */
+	if (pitch & 3) {
+		if (pitch + 3 < pitch) {
+			SDL_SetError("A scanline is too wide");
+			return(0);
+		}
+		pitch = (pitch + 3) & ~3;
+	}
+	if (pitch > 0xFFFF) {
+		SDL_SetError("A scanline is too wide");
+		return(0);
+	}
+	return((Uint16)pitch);
 }
 /*
  * Match an RGB value to a particular palette index
diff --git a/src/video/gapi/SDL_gapivideo.c b/src/video/gapi/SDL_gapivideo.c
index 86deadc..8a06485 100644
--- a/src/video/gapi/SDL_gapivideo.c
+++ b/src/video/gapi/SDL_gapivideo.c
@@ -733,6 +733,9 @@ SDL_Surface *GAPI_SetVideoMode(_THIS, SDL_Surface *current,
 	video->w = gapi->w = width;
 	video->h = gapi->h = height;
 	video->pitch = SDL_CalculatePitch(video); 
+	if (!current->pitch) {
+		return(NULL);
+	}
 
 	/* Small fix for WinCE/Win32 - when activating window
 	   SDL_VideoSurface is equal to zero, so activating code
diff --git a/src/video/nanox/SDL_nxvideo.c b/src/video/nanox/SDL_nxvideo.c
index b188e09..cbdd09a 100644
--- a/src/video/nanox/SDL_nxvideo.c
+++ b/src/video/nanox/SDL_nxvideo.c
@@ -378,6 +378,10 @@ SDL_Surface * NX_SetVideoMode (_THIS, SDL_Surface * current,
         current -> w = width ;
         current -> h = height ;
         current -> pitch = SDL_CalculatePitch (current) ;
+        if (!current->pitch) {
+            current = NULL;
+            goto done;
+        }
         NX_ResizeImage (this, current, flags) ;
     }
 
diff --git a/src/video/ps2gs/SDL_gsvideo.c b/src/video/ps2gs/SDL_gsvideo.c
index e172c60..3290866 100644
--- a/src/video/ps2gs/SDL_gsvideo.c
+++ b/src/video/ps2gs/SDL_gsvideo.c
@@ -479,6 +479,9 @@ static SDL_Surface *GS_SetVideoMode(_THIS, SDL_Surface *current,
 	current->w = width;
 	current->h = height;
 	current->pitch = SDL_CalculatePitch(current);
+	if (!current->pitch) {
+		return(NULL);
+	}
 
 	/* Memory map the DMA area for block memory transfer */
 	if ( ! mapped_mem ) {
diff --git a/src/video/ps3/SDL_ps3video.c b/src/video/ps3/SDL_ps3video.c
index d5519e0..17848e3 100644
--- a/src/video/ps3/SDL_ps3video.c
+++ b/src/video/ps3/SDL_ps3video.c
@@ -339,6 +339,9 @@ static SDL_Surface *PS3_SetVideoMode(_THIS, SDL_Surface * current, int width, in
 	current->w = width;
 	current->h = height;
 	current->pitch = SDL_CalculatePitch(current);
+	if (!current->pitch) {
+		return(NULL);
+	}
 
 	/* Alloc aligned mem for current->pixels */
 	s_pixels = memalign(16, current->h * current->pitch);
diff --git a/src/video/windib/SDL_dibvideo.c b/src/video/windib/SDL_dibvideo.c
index 6187bfc..86ebb12 100644
--- a/src/video/windib/SDL_dibvideo.c
+++ b/src/video/windib/SDL_dibvideo.c
@@ -675,6 +675,9 @@ SDL_Surface *DIB_SetVideoMode(_THIS, SDL_Surface *current,
 	video->w = width;
 	video->h = height;
 	video->pitch = SDL_CalculatePitch(video);
+	if (!current->pitch) {
+		return(NULL);
+	}
 
 	/* Small fix for WinCE/Win32 - when activating window
 	   SDL_VideoSurface is equal to zero, so activating code
diff --git a/src/video/windx5/SDL_dx5video.c b/src/video/windx5/SDL_dx5video.c
index f80ca97..39fc4fc 100644
--- a/src/video/windx5/SDL_dx5video.c
+++ b/src/video/windx5/SDL_dx5video.c
@@ -1127,6 +1127,9 @@ SDL_Surface *DX5_SetVideoMode(_THIS, SDL_Surface *current,
 		video->w = width;
 		video->h = height;
 		video->pitch = SDL_CalculatePitch(video);
+		if (!current->pitch) {
+			return(NULL);
+		}
 
 #ifndef NO_CHANGEDISPLAYSETTINGS
 		/* Set fullscreen mode if appropriate.
diff --git a/src/video/x11/SDL_x11video.c b/src/video/x11/SDL_x11video.c
index 79e60f9..45d1f79 100644
--- a/src/video/x11/SDL_x11video.c
+++ b/src/video/x11/SDL_x11video.c
@@ -1220,6 +1220,10 @@ SDL_Surface *X11_SetVideoMode(_THIS, SDL_Surface *current,
 		current->w = width;
 		current->h = height;
 		current->pitch = SDL_CalculatePitch(current);
+		if (!current->pitch) {
+			current = NULL;
+			goto done;
+		}
 		if (X11_ResizeImage(this, current, flags) < 0) {
 			current = NULL;
 			goto done;
-- 
2.20.1

