[U-Boot] [PATCH] fs: fat: fix fatwrite overflow calculation

[U-Boot] [PATCH] fs: fat: fix fatwrite overflow calculation

[Reno Farnesi]

The overflow calculation was incorrect. Adding the start block of the
partition is not needed because the sectors are already relative to the
beginning of the partition. If you attempted to write a file smaller
than cur_part_info.start blocks on a full partition the old calculation
fails to catch the overflow. This would cause an infinite loop in the
determine_fatent function.

Old, incorrect calculation:

ending sector of new file = start sector + file size (in sectors)
last sector = partition start + total sectors on the partition

Adding the partition start block number is not needed because sectors
are already relative to the start of the partition.

New calculation:

ending sector of new file = start sector + file size (in sectors)
last sector = total sectors on the partition

Signed-off-by: Reno Farnesi <nfarnesi4@gmail.com>
---

 fs/fat/fat_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index f6f06289f4..4ca024c208 100644
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -762,7 +762,7 @@ static int check_overflow(fsdata *mydata, __u32 clustnum, loff_t size)
 	if (offset != 0)
 		sect_num++;
 
-	if (startsect + sect_num > cur_part_info.start + total_sector)
+	if (startsect + sect_num > total_sector)
 		return -1;
 	return 0;
 }
-- 
2.13.3

[U-Boot] fs: fat: fix fatwrite overflow calculation

[Tom Rini]

On Sun, Aug 13, 2017 at 03:16:17PM -0400, Reno Farnesi wrote:

> The overflow calculation was incorrect. Adding the start block of the
> partition is not needed because the sectors are already relative to the
> beginning of the partition. If you attempted to write a file smaller
> than cur_part_info.start blocks on a full partition the old calculation
> fails to catch the overflow. This would cause an infinite loop in the
> determine_fatent function.
> 
> Old, incorrect calculation:
> 
> ending sector of new file = start sector + file size (in sectors)
> last sector = partition start + total sectors on the partition
> 
> Adding the partition start block number is not needed because sectors
> are already relative to the start of the partition.
> 
> New calculation:
> 
> ending sector of new file = start sector + file size (in sectors)
> last sector = total sectors on the partition
> 
> Signed-off-by: Reno Farnesi <nfarnesi4@gmail.com>

Applied to u-boot/master, thanks!

-- 
Tom
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