From 0ceef3d3710960347fde6c57f12f3de6fe9cfaaf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Tue, 6 Sep 2016 04:36:50 +0200
Subject: ext4: Avoid out-of-bounds access of block bitmap
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If the blocksize is 1024, count is initialized with 1. Incrementing count
by 8 will never match (count == fs->blksz * 8), and ptr may be
incremented beyond the buffer end if the bitmap is filled. Add the
startblock offset after the loop.

Remove the second loop, as only the first iteration will be done.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index db5cdb9..5e874af 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -163,18 +163,12 @@ static int _get_new_inode_no(unsigned char *buffer)
 
 static int _get_new_blk_no(unsigned char *buffer)
 {
-	unsigned char input;
-	int operand, status;
+	int operand;
 	int count = 0;
-	int j = 0;
+	int i;
 	unsigned char *ptr = buffer;
 	struct ext_filesystem *fs = get_fs();
 
-	if (fs->blksz != 1024)
-		count = 0;
-	else
-		count = 1;
-
 	while (*ptr == 255) {
 		ptr++;
 		count += 8;
@@ -182,21 +176,17 @@ static int _get_new_blk_no(unsigned char *buffer)
 			return -1;
 	}
 
-	for (j = 0; j < fs->blksz; j++) {
-		input = *ptr;
-		int i = 0;
-		while (i <= 7) {
-			operand = 1 << i;
-			status = input & operand;
-			if (status) {
-				i++;
-				count++;
-			} else {
-				*ptr |= operand;
-				return count;
-			}
+	if (fs->blksz == 1024)
+		count += 1;
+
+	for (i = 0; i <= 7; i++) {
+		operand = 1 << i;
+		if (*ptr & operand) {
+			count++;
+		} else {
+			*ptr |= operand;
+			return count;
 		}
-		ptr = ptr + 1;
 	}
 
 	return -1;
-- 
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