staging: erofs: add two missing erofs_workgroup_put for corrupted images

commit 138e1a09 upstream.

As reported by erofs-utils fuzzer, these error handling
path will be entered to handle corrupted images.

Lack of erofs_workgroup_puts will cause unmounting
unsuccessfully.

Fix these return values to EFSCORRUPTED as well.

Fixes: 3883a79a ("staging: erofs: introduce VLE decompression support")
Cc: <stable@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Link: https://lore.kernel.org/r/20190819103426.87579-4-gaoxiang25@huawei.com
[ Gao Xiang: Older kernel versions don't have length validity check
             and EFSCORRUPTED, thus backport pageofs check for now. ]
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/unzip_vle.c

@@ -311,7 +311,11 @@ z_erofs_vle_work_lookup(struct super_block *sb,
 	/* if multiref is disabled, `primary' is always true */
 	primary = true;
 
-	DBG_BUGON(work->pageofs != pageofs);
+	if (work->pageofs != pageofs) {
+		DBG_BUGON(1);
+		erofs_workgroup_put(egrp);
+		return ERR_PTR(-EIO);
+	}
 
 	/*
 	 * lock must be taken first to avoid grp->next == NIL between