[PATCH net-next] ptr_ring: fix integer overflow

[Jason Wang]

We try to allocate one more entry for lockless peeking. The adding
operation may overflow which causes zero to be passed to kmalloc().
In this case, it returns ZERO_SIZE_PTR without any notice by ptr
ring. Try to do producing or consuming on such ring will lead NULL
dereference. Fix this detect and fail early.

Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
Reported-by: syzbot+87678bcf753b44c39b67@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 include/linux/ptr_ring.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 9ca1726..3f99484 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -453,6 +453,8 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
 
 static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
 {
+	if (unlikely(size + 1 == 0))
+		return NULL;
 	/* Allocate an extra dummy element at end of ring to avoid consumer head
 	 * or produce head access past the end of the array. Possible when
 	 * producer/consumer operations and __ptr_ring_peek operations run in
-- 
2.7.4