netdev - [PATCH net-next] net: expand NETDEV_RSS_KEY

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20260122190349.2771064-1-edumazet@google.com>
Date: Thu, 22 Jan 2026 19:03:49 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] net: expand NETDEV_RSS_KEY_LEN to 256 bytes

NETDEV_RSS_KEY_LEN has been set to 52 bytes in 2014, until now.

Jakub suggested we bump the size to 128 bytes or more.

Some drivers (like idpf) were already working around the core limit.

Since this change might cause some issues in admin scripts,
bump it directly to 256 in one go.

tjbp26:~# cat /proc/sys/net/core/netdev_rss_key | wc -c
768

tjbp26:~# ethtool -x eth1
RX flow hash indirection table for eth1 with 32 RX ring(s):
...
RSS hash key:
fe:16:5b:2f:93:85:c2:c9:c1:ef:bd:60:c6:e0:2b:99:4d:bf:b7:14:c8:1e:8d:cb:31:17:51:da:55:eb:91:d9:9e:f9:89:9b:44:a1:dc:08:72:3a:b3:d6:31:86:9a:fe:02:3a:0d:eb:a1:7c:f5:a3:51:3b:08:56:c9:3f:71:69:01:ba:70:38
RSS hash function:
    toeplitz: on
    xor: off
    crc32: off

Suggested-by: Jakub Kicinski <kuba@...nel.org>
Link: https://lore.kernel.org/netdev/20260122075206.504ec591@kernel.org/
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 Documentation/admin-guide/sysctl/net.rst | 13 +++++++------
 include/linux/netdevice.h                |  3 +--
 net/core/sysctl_net_core.c               | 10 ++++++++--
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 91fa4ccd326c2b6351fd028a1c5d1c69126bee5f..19408da2390b013b06ca92b16c152d48a5efbc1e 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -314,21 +314,22 @@ Default: 1000
 netdev_rss_key
 --------------
 
-RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is
-randomly generated.
+RSS (Receive Side Scaling) enabled drivers use a host key that
+is randomly generated.
 Some user space might need to gather its content even if drivers do not
 provide ethtool -x support yet.
 
 ::
 
   myhost:~# cat /proc/sys/net/core/netdev_rss_key
-  84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (52 bytes total)
+  84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (256 bytes total)
 
-File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
+File contains all nul bytes if no driver ever called netdev_rss_key_fill()
+function.
 
 Note:
-  /proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
-  but most drivers only use 40 bytes of it.
+  /proc/sys/net/core/netdev_rss_key contains 256 bytes of key,
+  but many drivers only use 40 or 52 bytes of it.
 
 ::
 
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d99b0fbc1942ad1dbbd372cfb9e809e413251f15..3524c54c786a94a1e797c07d6b2d1cf35b6cbc5b 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -5163,8 +5163,7 @@ void *netdev_lower_dev_get_private(struct net_device *dev,
 void netdev_lower_state_changed(struct net_device *lower_dev,
 				void *lower_state_info);
 
-/* RSS keys are 40 or 52 bytes long */
-#define NETDEV_RSS_KEY_LEN 52
+#define NETDEV_RSS_KEY_LEN 256
 extern u8 netdev_rss_key[NETDEV_RSS_KEY_LEN] __read_mostly;
 void netdev_rss_key_fill(void *buffer, size_t len);
 
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 05dd55cf8b58e6c6fce498a11c09f23fd56d8f34..0f761d4b94471a5f8bbe0810922cf59e009be99d 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -325,10 +325,16 @@ static int proc_do_dev_weight(const struct ctl_table *table, int write,
 static int proc_do_rss_key(const struct ctl_table *table, int write,
 			   void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct ctl_table fake_table;
 	char buf[NETDEV_RSS_KEY_LEN * 3];
+	struct ctl_table fake_table;
+	char *pos = buf;
+
+	for (int i = 0; i < NETDEV_RSS_KEY_LEN; i++) {
+		pos = hex_byte_pack(pos, netdev_rss_key[i]);
+		*pos++ = ':';
+	}
+	*(--pos) = 0;
 
-	snprintf(buf, sizeof(buf), "%*phC", NETDEV_RSS_KEY_LEN, netdev_rss_key);
 	fake_table.data = buf;
 	fake_table.maxlen = sizeof(buf);
 	return proc_dostring(&fake_table, write, buffer, lenp, ppos);
-- 
2.52.0.457.g6b5491de43-goog