[PATCH for-4.19 1/4] staging: erofs: fix an error handling in erofs_readdir()

[Gao Xiang]

commit acb383f1dcb4f1e79b66d4be3a0b6f519a957b0d upstream.

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+
Reviewed-by: Chao Yu <yuchao0 at huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
Link: https://lore.kernel.org/r/20190818125457.25906-1-hsiangkao@aol.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
[ Gao Xiang: Since earlier kernels don't define EFSCORRUPTED,
             let's use original error code instead. ]
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
---

Compared with 5.3.y series, 
"staging: erofs: avoid endless loop of invalid lookback distance 0"
isn't included in this series since 4.19 is quite different from the
current code, no simple fix for this (used for corruptted images).
I will try a full fix later.

 drivers/staging/erofs/dir.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/erofs/dir.c b/drivers/staging/erofs/dir.c
index 0a089cf5c78f..fe6683effd05 100644
--- a/drivers/staging/erofs/dir.c
+++ b/drivers/staging/erofs/dir.c
@@ -100,8 +100,15 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
 		unsigned 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 = PTR_ERR(dentry_page);
+			break;
+		}
 
 		lock_page(dentry_page);
 		de = (struct erofs_dirent *)kmap(dentry_page);
-- 
2.17.1