[PATCH 5.10 340/529] exfat: fix reporting fs error when reading dir beyond EOF

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From: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>

commit 706fdcac002316893434d753be8cfb549fe1d40d upstream.

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()")
Cc: stable@xxxxxxxxxxxxxxx # v5.7+
Signed-off-by: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>
Reviewed-by: Andy Wu <Andy.Wu@xxxxxxxx>
Reviewed-by: Aoyama Wataru <wataru.aoyama@xxxxxxxx>
Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/exfat/dir.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -102,7 +102,7 @@ static int exfat_readdir(struct inode *i
 			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;
 





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