Subject: Re: [PATCH net 3/7] net/handshake: Pass negative errno through handshake_complete()

From: Jakub Kicinski <[email-masked]>
Date: Wed, 20 May 2026 19:39:46 -0700

On Mon, 18 May 2026 14:24:30 -0400 Chuck Lever wrote:
> -	if (info->attrs[HANDSHAKE_A_DONE_STATUS])
> -		status = nla_get_u32(info->attrs[HANDSHAKE_A_DONE_STATUS]);
> +	if (info->attrs[HANDSHAKE_A_DONE_STATUS]) {
> +		u32 val = nla_get_u32(info->attrs[HANDSHAKE_A_DONE_STATUS]);
> +
> +		/* Values above MAX_ERRNO would overflow on negation. */
> +		if (val <= MAX_ERRNO)
> +			status = -(int)val;
> +	}

Why not set a policy so that user space can't pass invalid stuff?

(note - sashiko has some more comments but AFAICT they are either
addressed throughout the series or false positives)

diff --git a/Documentation/netlink/specs/handshake.yaml b/Documentation/netlink/specs/handshake.yaml
index 95c3fade7a8d..1024297b3851 100644
--- a/Documentation/netlink/specs/handshake.yaml
+++ b/Documentation/netlink/specs/handshake.yaml
@@ -12,6 +12,12 @@ protocol: genetlink
 doc: Netlink protocol to request a transport layer security handshake.
 
 definitions:
+  -
+    type: const
+    name: max-errno
+    value: 4095
+    header: linux/err.h
+    scope: kernel
   -
     type: enum
     name: handler-class
@@ -80,6 +86,8 @@ doc: Netlink protocol to request a transport layer security handshake.
       -
         name: status
         type: u32
+        checks:
+          max: max-errno
       -
         name: sockfd
         type: s32
diff --git a/net/handshake/genl.h b/net/handshake/genl.h
index 8d3e18672daf..46b65f131669 100644
--- a/net/handshake/genl.h
+++ b/net/handshake/genl.h
@@ -11,6 +11,7 @@
 #include <net/genetlink.h>
 
 #include <uapi/linux/handshake.h>
+#include <linux/err.h>
 
 int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info);
 int handshake_nl_done_doit(struct sk_buff *skb, struct genl_info *info);
diff --git a/net/handshake/genl.c b/net/handshake/genl.c
index 870612609491..4b20cd9cdd0e 100644
--- a/net/handshake/genl.c
+++ b/net/handshake/genl.c
@@ -10,6 +10,7 @@
 #include "genl.h"
 
 #include <uapi/linux/handshake.h>
+#include <linux/err.h>
 
 /* HANDSHAKE_CMD_ACCEPT - do */
 static const struct nla_policy handshake_accept_nl_policy[HANDSHAKE_A_ACCEPT_HANDLER_CLASS + 1] = {
@@ -18,7 +19,7 @@ static const struct nla_policy handshake_accept_nl_policy[HANDSHAKE_A_ACCEPT_HAN
 
 /* HANDSHAKE_CMD_DONE - do */
 static const struct nla_policy handshake_done_nl_policy[HANDSHAKE_A_DONE_REMOTE_AUTH + 1] = {
-	[HANDSHAKE_A_DONE_STATUS] = { .type = NLA_U32, },
+	[HANDSHAKE_A_DONE_STATUS] = NLA_POLICY_MAX(NLA_U32, MAX_ERRNO),
 	[HANDSHAKE_A_DONE_SOCKFD] = { .type = NLA_S32, },
 	[HANDSHAKE_A_DONE_REMOTE_AUTH] = { .type = NLA_U32, },
 };