From b352caea752f9e840863ade43da67ff0272e8594 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Thu, 26 Jan 2017 20:22:36 +0000
Subject: fs/fat: Fix unaligned __u16 reads for FAT12 access
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Doing unaligned reads is not supported on all architectures, use
byte sized reads of the little endian buffer.
Rename off16 to off8, as it reflects the buffer offset in byte
granularity (offset is in entry, i.e. 12 bit, granularity).
Fix a regression introduced in 8d48c92b45aea91e2a2be90f2ed93677e85526f1

Reported-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Tested-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 244ee09..5654003 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -179,7 +179,7 @@ int flush_dirty_fat_buffer(fsdata *mydata)
 static __u32 get_fatent(fsdata *mydata, __u32 entry)
 {
 	__u32 bufnum;
-	__u32 off16, offset;
+	__u32 offset, off8;
 	__u32 ret = 0x00;
 
 	if (CHECK_CLUST(entry, mydata->fatsize)) {
@@ -242,8 +242,9 @@ static __u32 get_fatent(fsdata *mydata, __u32 entry)
 		ret = FAT2CPU16(((__u16 *) mydata->fatbuf)[offset]);
 		break;
 	case 12:
-		off16 = (offset * 3) / 2;
-		ret = FAT2CPU16(*(__u16 *)(mydata->fatbuf + off16));
+		off8 = (offset * 3) / 2;
+		/* fatbut + off8 may be unaligned, read in byte granularity */
+		ret = mydata->fatbuf[off8] + (mydata->fatbuf[off8 + 1] << 8);
 
 		if (offset & 0x1)
 			ret >>= 4;
-- 
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