[U-Boot] [PATCH v2] fs/fat: Fix unaligned __u16 reads for FAT12 access

[U-Boot] [PATCH v2] fs/fat: Fix unaligned __u16 reads for FAT12 access

[Brüns, Stefan]

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 Br?ns <stefan.bruens@rwth-aachen.de>
Tested-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>
---
 fs/fat/fat.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

v2: added parentheses to fix operator precedence
    added Tested-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index fe899d0442..23ec280071 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;
-- 
2.11.0

[U-Boot] [U-Boot, v2] fs/fat: Fix unaligned __u16 reads for FAT12 access

[Tom Rini]

On Thu, Jan 26, 2017 at 08:22:36PM +0000, Stefan Br?ns wrote:

> 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 Br?ns <stefan.bruens@rwth-aachen.de>
> Tested-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>

Applied to u-boot/master, thanks!

-- 
Tom
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