fs/fat: Avoid corruption of sectors following the FAT
The FAT is read/flushed in segments of 6 (FATBUFBLOCKS) disk sectors. The
last segment may be less than 6 sectors, cap the length.
Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>
diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index df9f2b5..6319581 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -202,6 +202,7 @@
__u32 fatlength = mydata->fatlength;
__u32 startblock = bufnum * FATBUFBLOCKS;
+ /* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
if (startblock + getsize > fatlength)
getsize = fatlength - startblock;
diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index aab0b0e..4605020 100644
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -117,10 +117,11 @@
if ((!mydata->fat_dirty) || (mydata->fatbufnum == -1))
return 0;
- startblock += mydata->fat_sect;
+ /* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
+ if (startblock + getsize > fatlength)
+ getsize = fatlength - startblock;
- if (getsize > fatlength)
- getsize = fatlength;
+ startblock += mydata->fat_sect;
/* Write FAT buf */
if (disk_write(startblock, getsize, bufptr) < 0) {
@@ -187,8 +188,9 @@
__u32 fatlength = mydata->fatlength;
__u32 startblock = bufnum * FATBUFBLOCKS;
- if (getsize > fatlength)
- getsize = fatlength;
+ /* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
+ if (startblock + getsize > fatlength)
+ getsize = fatlength - startblock;
startblock += mydata->fat_sect; /* Offset from start of disk */
@@ -499,15 +501,15 @@
__u32 fatlength = mydata->fatlength;
__u32 startblock = bufnum * FATBUFBLOCKS;
- fatlength *= mydata->sect_size;
- startblock += mydata->fat_sect;
-
- if (getsize > fatlength)
- getsize = fatlength;
+ /* Cap length if fatlength is not a multiple of FATBUFBLOCKS */
+ if (startblock + getsize > fatlength)
+ getsize = fatlength - startblock;
if (flush_dirty_fat_buffer(mydata) < 0)
return -1;
+ startblock += mydata->fat_sect;
+
if (disk_read(startblock, getsize, bufptr) < 0) {
debug("Error reading FAT blocks\n");
return -1;