[PATCH v2] staging: erofs: fix an error handling in erofs_readdir()

[Gao Xiang]

From: Gao Xiang <gaoxiang25 at huawei.com>

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 at nod.at>
Fixes: 3aa8ec716e52 ("staging: erofs: add directory operations")
Cc: <stable at vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
---

changelog from v1:
 - fix the incorrect external link in commit message.

This patch is based on the following patch as well
https://lore.kernel.org/r/20190816071142.8633-1-gaoxiang25@huawei.com/

and
https://lore.kernel.org/r/20190817082313.21040-1-hsiangkao@aol.com/
can still be properly applied after this patch.

 drivers/staging/erofs/dir.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/erofs/dir.c b/drivers/staging/erofs/dir.c
index 5f38382637e6..f2d7539589e4 100644
--- a/drivers/staging/erofs/dir.c
+++ b/drivers/staging/erofs/dir.c
@@ -82,8 +82,12 @@ 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 (IS_ERR(dentry_page)) {
+			errln("fail to readdir of logical block %u of nid %llu",
+			      i, EROFS_V(dir)->nid);
+			err = PTR_ERR(dentry_page);
+			break;
+		}
 
 		de = (struct erofs_dirent *)kmap(dentry_page);
 
-- 
2.17.1