[PATCH v1] exfat: fix reporting fs error when reading dir beyond EOF

[Yuezhang.Mo@xxxxxxxx]

Since seekdir() does not check whether the position is valid, the
position may exceed the size of the directory. We found that for
a directory with discontinuous clusters, if the position exceeds
the size of the directory and the excess size is greater than or
equal to the cluster size, exfat_readdir() will return -EIO,
causing a file system error and making the file system unavailable.

Reproduce this bug by:

seekdir(dir, dir_size + cluster_size);
dirent = readdir(dir);

The following log will be printed if mount with 'errors=remount-ro'.

[11166.712896] exFAT-fs (sdb1): error, invalid access to FAT (entry 0xffffffff)
[11166.712905] exFAT-fs (sdb1): Filesystem has been set read-only

Fixes: 1e5654de0f51 ("exfat: handle wrong stream entry size in exfat_readdir()")

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>
Reviewed-by: Andy Wu <Andy.Wu@xxxxxxxx>
Reviewed-by: Aoyama Wataru <wataru.aoyama@xxxxxxxx>
---
 fs/exfat/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 1122bee3b634..158427e8124e 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -100,7 +100,7 @@ static int exfat_readdir(struct inode *inode, loff_t *cpos, struct exfat_dir_ent
 			clu.dir = ei->hint_bmap.clu;
 		}
 
-		while (clu_offset > 0) {
+		while (clu_offset > 0 && clu.dir != EXFAT_EOF_CLUSTER) {
 			if (exfat_get_next_cluster(sb, &(clu.dir)))
 				return -EIO;
 
-- 
2.25.1