[PATCH 5.4 12/33] udp: Prevent reuseport_select_sock from reading uninitialized socks

[Greg Kroah-Hartman]

From: Baptiste Lepers <baptiste.lepers@xxxxxxxxx>

[ Upstream commit fd2ddef043592e7de80af53f47fa46fd3573086e ]

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@xxxxxxxxx>
Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210107051110.12247-1-baptiste.lepers@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/core/sock_reuseport.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -302,7 +302,7 @@ 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;