udp: Prevent reuseport_select_sock from reading uninitialized socks

reuse->socks[] is modified concurrently by reuseport_add_sock. To
prevent reading values that have not been fully initialized, only read
the array up until the last known safe index instead of incorrectly
re-reading the last index of the array.

Fixes: acdcecc61285f ("udp: correct reuseport selection with connected sockets")
Signed-off-by: Baptiste Lepers <baptiste.lepers@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20210107051110.12247-1-baptiste.lepers@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index bbdd3c7b6cb5b960e4d107c3f25e7067db938483..b065f0a103ed06e40105967b9926679d5840d00a 100644 (file)
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -293,7 +293,7 @@ select_by_hash:
                        i = j = reciprocal_scale(hash, socks);
                        while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {
                                i++;
-                               if (i >= reuse->num_socks)
+                               if (i >= socks)
                                        i = 0;
                                if (i == j)
                                        goto out;