[PATCH] 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 <redacted>
---
 net/core/sock_reuseport.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index bbdd3c7b6cb5..b065f0a103ed 100644
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c

@@ -293,7 +293,7 @@ struct sock *reuseport_select_sock(struct sock *sk,
 			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;

-- 
2.17.1

On Thu, Jan 7, 2021 at 12:11 AM Baptiste Lepers
[off-list ref] wrote:

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 <redacted>

Acked-by: Willem de Bruijn <willemb@google.com>

Thanks. This also matches local variable socks as used to calculate i
and j with reciprocal_scale immediately above.

Please mark fixes [PATCH net] in the future.

On Thu, 7 Jan 2021 00:27:07 -0500 Willem de Bruijn wrote:

On Thu, Jan 7, 2021 at 12:11 AM Baptiste Lepers
[off-list ref] wrote:

quoted

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 <redacted>  

Acked-by: Willem de Bruijn <willemb@google.com>

Thanks. This also matches local variable socks as used to calculate i
and j with reciprocal_scale immediately above.

Please mark fixes [PATCH net] in the future.

And please don't wrap the fixes tags.

Applied, thanks!