exfat: fix uninit-value in __exfat_get_dentry_set

BugLink: https://bugs.launchpad.net/bugs/2101915

commit 02dffe9ab092fc4c8800aee68cb7eafd37a980c4 upstream.

There is no check if stream size and start_clu are invalid.
If start_clu is EOF cluster and stream size is 4096, It will
cause uninit value access. because ei->hint_femp.eidx could
be 128(if cluster size is 4K) and wrong hint will allocate
next cluster. and this cluster will be same with the cluster
that is allocated by exfat_extend_valid_size(). The previous
patch will check invalid start_clu, but for clarity, initialize
hint_femp.eidx to zero.

Cc: [email protected]
Reported-by: [email protected]
Tested-by: [email protected]
Reviewed-by: Yuezhang Mo <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Koichiro Den <[email protected]>
Signed-off-by: Stefan Bader <[email protected]>

Author: namjaejeon

fs/exfat/namei.c

@@ -377,6 +377,7 @@ static int exfat_find_empty_entry(struct inode *inode,
 		if (ei->start_clu == EXFAT_EOF_CLUSTER) {
 			ei->start_clu = clu.dir;
 			p_dir->dir = clu.dir;
+			hint_femp.eidx = 0;
 		}
 
 		/* append to the FAT chain */