net: sk_prot_alloc() should not blindly overwrite memory
Some sockets use SLAB_DESTROY_BY_RCU, and our RCU code correctness
depends on sk->sk_nulls_node.next being always valid. A NULL
value is not allowed as it might fault a lockless reader.
Current sk_prot_alloc() implementation doesnt respect this hypothesis,
calling kmem_cache_alloc() with __GFP_ZERO. Just call memset() around
the forbidden field.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/sock.c b/net/core/sock.c
index 6354863..ba5d211 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -939,8 +939,23 @@
struct kmem_cache *slab;
slab = prot->slab;
- if (slab != NULL)
- sk = kmem_cache_alloc(slab, priority);
+ if (slab != NULL) {
+ sk = kmem_cache_alloc(slab, priority & ~__GFP_ZERO);
+ if (!sk)
+ return sk;
+ if (priority & __GFP_ZERO) {
+ /*
+ * caches using SLAB_DESTROY_BY_RCU should let
+ * sk_node.next un-modified. Special care is taken
+ * when initializing object to zero.
+ */
+ if (offsetof(struct sock, sk_node.next) != 0)
+ memset(sk, 0, offsetof(struct sock, sk_node.next));
+ memset(&sk->sk_node.pprev, 0,
+ prot->obj_size - offsetof(struct sock,
+ sk_node.pprev));
+ }
+ }
else
sk = kmalloc(prot->obj_size, priority);
