netdev - [PATCH net-next 05/12] ptr_ring: disallow lockless __ptr_ring

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Date:   Fri, 26 Jan 2018 01:36:32 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        David Miller <davem@...emloft.net>
Subject: [PATCH net-next 05/12] ptr_ring: disallow lockless __ptr_ring_full

Similar to bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can
overrun array bounds") a lockless use of __ptr_ring_full might
cause an out of bounds access.

We can fix this, but it's easier to just disallow lockless
__ptr_ring_full for now.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 include/linux/ptr_ring.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 9a72d8f..f175846 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -45,9 +45,10 @@ struct ptr_ring {
 };
 
 /* Note: callers invoking this in a loop must use a compiler barrier,
- * for example cpu_relax().  If ring is ever resized, callers must hold
- * producer_lock - see e.g. ptr_ring_full.  Otherwise, if callers don't hold
- * producer_lock, the next call to __ptr_ring_produce may fail.
+ * for example cpu_relax().
+ *
+ * NB: this is unlike __ptr_ring_empty in that callers must hold producer_lock:
+ * see e.g. ptr_ring_full.
  */
 static inline bool __ptr_ring_full(struct ptr_ring *r)
 {
-- 
MST