fs/fat: correct FAT16/12 file finding in root dir

When write a file into FAT file system, it will search a match file in
root dir. So the find_directory_entry() will get the first cluster of
root dir content and search the directory item one by one. If the file
is not found, we will call get_fatent_value() to get next cluster of root
dir via lookup the FAT table and continue the search.

The issue is in FAT16/12 system, we cannot get root dir's next clust
from FAT table. The FAT table only be use to find the clust of data
aera in FAT16/12.

In FAT16/12 if the clust is in root dir, the clust number is a negative
number or 0, 1. Since root dir is located in front of the data area.
Data area start clust #2. So the root dir clust number should < 2.

This patch will check above situation before call get_fatenv_value().
If curclust is < 2, include minus number, we just increase one on the
curclust since root dir is in continous cluster.

The patch also add a sanity check for entry in get_fatenv_value().

Signed-off-by: Josh Wu <josh.wu@atmel.com>

diff --git a/fs/fat/fat_write.c b/fs/fat/fat_write.c
index 90d6ab63bf7731ee7088ede6a9a7be2fc495f412..ba7e3aeb0b62ccf46495e012b3bceeae01b1c039 100644 (file)
--- a/fs/fat/fat_write.c
+++ b/fs/fat/fat_write.c
@@ -139,6 +139,11 @@ static __u32 get_fatent_value(fsdata *mydata, __u32 entry)
        __u32 ret = 0x00;
        __u16 val1, val2;
 
+       if (CHECK_CLUST(entry, mydata->fatsize)) {
+               printf("Error: Invalid FAT entry: 0x%08x\n", entry);
+               return ret;
+       }
+
        switch (mydata->fatsize) {
        case 32:
                bufnum = entry / FAT32BUFSIZE;
@@ -881,6 +886,28 @@ static dir_entry *find_directory_entry(fsdata *mydata, int startsect,
                        return dentptr;
                }
 
+               /*
+                * In FAT16/12, the root dir is locate before data area, shows
+                * in following:
+                * -------------------------------------------------------------
+                * | Boot | FAT1 & 2 | Root dir | Data (start from cluster #2) |
+                * -------------------------------------------------------------
+                *
+                * As a result if curclust is in Root dir, it is a negative
+                * number or 0, 1.
+                *
+                */
+               if (mydata->fatsize != 32 && (int)curclust <= 1) {
+                       /* Current clust is in root dir, set to next clust */
+                       curclust++;
+                       if ((int)curclust <= 1)
+                               continue;       /* continue to find */
+
+                       /* Reach the end of root dir */
+                       empty_dentptr = dentptr;
+                       return NULL;
+               }
+
                curclust = get_fatent_value(mydata, dir_curclust);
                if (IS_LAST_CLUST(curclust, mydata->fatsize)) {
                        empty_dentptr = dentptr;