staging: erofs: fix an error handling in erofs_readdir()

Richard observed a forever loop of erofs_read_raw_page() [1]
which can be generated by forcely setting ->u.i_blkaddr
to 0xdeadbeef (as my understanding block layer can
handle access beyond end of device correctly).

After digging into that, it seems the problem is highly
related with directories and then I found the root cause
is an improper error handling in erofs_readdir().

Let's fix it now.

[1] https://lore.kernel.org/r/1163995781.68824.1566084358245.JavaMail.zimbra@nod.at/

Reported-by: Richard Weinberger <richard@nod.at>
Fixes: 3aa8ec716e52 ("staging: erofs: add directory operations")
Cc: <stable@vger.kernel.org> # 4.19+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190818125457.25906-1-hsiangkao@aol.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/erofs/dir.c b/drivers/staging/erofs/dir.c
index 5f38382637e6cbcbdf5b9ea1350506cd9466368c..77ef856df9f3a5f7caa9fddf95599af697759aea 100644 (file)
--- a/drivers/staging/erofs/dir.c
+++ b/drivers/staging/erofs/dir.c
@@ -82,8 +82,15 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
                unsigned int nameoff, maxsize;
 
                dentry_page = read_mapping_page(mapping, i, NULL);
-               if (IS_ERR(dentry_page))
-                       continue;
+               if (dentry_page == ERR_PTR(-ENOMEM)) {
+                       err = -ENOMEM;
+                       break;
+               } else if (IS_ERR(dentry_page)) {
+                       errln("fail to readdir of logical block %u of nid %llu",
+                             i, EROFS_V(dir)->nid);
+                       err = -EFSCORRUPTED;
+                       break;
+               }
 
                de = (struct erofs_dirent *)kmap(dentry_page);