[PATCH] erofs: fix a potential NULL dereference of alloc_pages()

[xkernel.wang at foxmail.com]

From: Xiaoke Wang <xkernel.wang at foxmail.com>

alloc_pages() returns the page on success or NULL if allocation fails,
while set_page_private() will dereference `newpage`. So it is better to
catch the memory error in case other errors happen.

Signed-off-by: Xiaoke Wang <xkernel.wang at foxmail.com>
---
 fs/erofs/zdata.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 11c7a1a..36a5421 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -735,11 +735,15 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 		struct page *const newpage =
 				alloc_page(GFP_NOFS | __GFP_NOFAIL);
 
-		set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
-		err = z_erofs_attach_page(clt, newpage,
-					  Z_EROFS_PAGE_TYPE_EXCLUSIVE);
-		if (!err)
-			goto retry;
+		if (!newpage) {
+			err = -ENOMEM;
+		} else {
+			set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
+			err = z_erofs_attach_page(clt, newpage,
+						Z_EROFS_PAGE_TYPE_EXCLUSIVE);
+			if (!err)
+				goto retry;
+		}
 	}
 
 	if (err)
--