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 <col...@suse.de>
Cc: Chaitanya Kulkarni <chaitanya.kulka...@wdc.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Hannes Reinecke <h...@suse.de>
Cc: Jan Kara <j...@suse.com>
Cc: Jens Axboe <ax...@kernel.dk>
Cc: Mikhail Skorzhinskii <mskorzhins...@solarflare.com>
Cc: Philipp Reisner <philipp.reis...@linbit.com>
Cc: Sagi Grimberg <s...@grimberg.me>
Cc: Vlastimil Babka <vba...@suse.com>
Cc: sta...@vger.kernel.org
---
include/linux/net.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/include/linux/net.h b/include/linux/net.h
index d48ff1180879..ae713c851342 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
