Date:   Sun, 16 Aug 2020 15:15:15 +0800
From:   Coly Li <colyli@...e.de>
To:     linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, Coly Li <colyli@...e.de>,
        Chaitanya Kulkarni <chaitanya.kulkarni@....com>,
        Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
        Jan Kara <jack@...e.com>, Jens Axboe <axboe@...nel.dk>,
        Mikhail Skorzhinskii <mskorzhinskiy@...arflare.com>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Vlastimil Babka <vbabka@...e.com>
Subject: [PATCH v5 1/3] net: introduce helper sendpage_ok() in include/linux/net.h

The original problem was from nvme-over-tcp code, who mistakenly uses
kernel_sendpage() to send pages allocated by __get_free_pages() without
__GFP_COMP flag. Such pages don't have refcount (page_count is 0) on
tail pages, sending them by kernel_sendpage() may trigger a kernel panic
from a corrupted kernel heap, because these pages are incorrectly freed
in network stack as page_count 0 pages.

This patch introduces a helper sendpage_ok(), it returns true if the
checking page,
- is not slab page: PageSlab(page) is false.
- has page refcount: page_count(page) is not zero

All drivers who want to send page to remote end by kernel_sendpage()
may use this helper to check whether the page is OK. If the helper does
not return true, the driver should try other non sendpage method (e.g.
sock_no_sendpage()) to handle the page.

Signed-off-by: Coly Li <colyli@...e.de>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@....com>
Cc: Christoph Hellwig <hch@....de>
Cc: Hannes Reinecke <hare@...e.de>
Cc: Jan Kara <jack@...e.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Mikhail Skorzhinskii <mskorzhinskiy@...arflare.com>
Cc: Philipp Reisner <philipp.reisner@...bit.com>
Cc: Sagi Grimberg <sagi@...mberg.me>
Cc: Vlastimil Babka <vbabka@...e.com>
Cc: stable@...r.kernel.org
---
Changelog:
v5, include linux/mm.h in include/linux/net.h
v4, change sendpage_ok() as an inline helper, and post it as
    separate patch.
v3, introduce a more common sendpage_ok()
v2, fix typo in patch subject
v1, the initial version.
 include/linux/net.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/net.h b/include/linux/net.h
index d48ff1180879..a807fad31958 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -21,6 +21,7 @@
 #include <linux/rcupdate.h>
 #include <linux/once.h>
 #include <linux/fs.h>
+#include <linux/mm.h>
 #include <linux/sockptr.h>
 
 #include <uapi/linux/net.h>
@@ -286,6 +287,21 @@ do {									\
 #define net_get_random_once_wait(buf, nbytes)			\
 	get_random_once_wait((buf), (nbytes))
 
+/*
+ * E.g. XFS meta- & log-data is in slab pages, or bcache meta
+ * data pages, or other high order pages allocated by
+ * __get_free_pages() without __GFP_COMP, which have a page_count
+ * of 0 and/or have PageSlab() set. We cannot use send_page for
+ * those, as that does get_page(); put_page(); and would cause
+ * either a VM_BUG directly, or __page_cache_release a page that
+ * would actually still be referenced by someone, leading to some
+ * obscure delayed Oops somewhere else.
+ */
+static inline bool sendpage_ok(struct page *page)
+{
+	return  (!PageSlab(page) && page_count(page) >= 1);
+}
+
 int kernel_sendmsg(struct socket *sock, struct msghdr *msg, struct kvec *vec,
 		   size_t num, size_t len);
 int kernel_sendmsg_locked(struct sock *sk, struct msghdr *msg,
-- 
2.26.2

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