The code for handing file overwrite incorrectly assumed that the file on
disk is always contiguous. This resulted in corrupting disk structure
every time when write to existing fragmented file happened. Fix this
by adding proper check for cluster discontinuity and adjust chunk size
on each partial write.

Signed-off-by: Marek Szyprowski <[email protected]>
---
 fs/fat/fat_write.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index 729cf39630d..6cfa5b45652 100644
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -794,6 +794,8 @@ set_contents(fsdata *mydata, dir_entry *dentptr, loff_t 
pos, __u8 *buffer,
 
                        newclust = get_fatent(mydata, endclust);
 
+                       if ((newclust - 1) != endclust)
+                               break;
                        if (IS_LAST_CLUST(newclust, mydata->fatsize))
                                break;
                        if (CHECK_CLUST(newclust, mydata->fatsize)) {
@@ -811,7 +813,7 @@ set_contents(fsdata *mydata, dir_entry *dentptr, loff_t 
pos, __u8 *buffer,
                        offset = 0;
                else
                        offset = pos - cur_pos;
-               wsize = min(cur_pos + actsize, filesize) - pos;
+               wsize = min_t(unsigned long long, actsize, filesize - cur_pos);
                if (get_set_cluster(mydata, curclust, offset,
                                    buffer, wsize, &actsize)) {
                        printf("Error get-and-setting cluster\n");
@@ -824,8 +826,6 @@ set_contents(fsdata *mydata, dir_entry *dentptr, loff_t 
pos, __u8 *buffer,
                if (filesize <= cur_pos)
                        break;
 
-               /* CHECK: newclust = get_fatent(mydata, endclust); */
-
                if (IS_LAST_CLUST(newclust, mydata->fatsize))
                        /* no more clusters */
                        break;
-- 
2.17.1

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