netdev - Re: [PATCH] [v2] myri10ge: avoid uninitialized variable use

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Message-ID: <20250622162715.GA297140@horms.kernel.org>
Date: Sun, 22 Jun 2025 17:27:15 +0100
From: Simon Horman <horms@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] myri10ge: avoid uninitialized variable use

On Sat, Jun 21, 2025 at 09:35:11PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> While compile testing on less common architectures, I noticed that gcc-10 on
> s390 finds a bug that all other configurations seem to miss:
> 
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c: In function 'myri10ge_set_multicast_list':
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c:391:25: error: 'cmd.data0' is used uninitialized in this function [-Werror=uninitialized]
>   391 |  buf->data0 = htonl(data->data0);
>       |                         ^~
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c:392:25: error: '*((void *)&cmd+4)' is used uninitialized in this function [-Werror=uninitialized]
>   392 |  buf->data1 = htonl(data->data1);
>       |                         ^~
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c: In function 'myri10ge_allocate_rings':
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c:392:13: error: 'cmd.data1' is used uninitialized in this function [-Werror=uninitialized]
>   392 |  buf->data1 = htonl(data->data1);
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c:1939:22: note: 'cmd.data1' was declared here
>  1939 |  struct myri10ge_cmd cmd;
>       |                      ^~~
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c:393:13: error: 'cmd.data2' is used uninitialized in this function [-Werror=uninitialized]
>   393 |  buf->data2 = htonl(data->data2);
> drivers/net/ethernet/myricom/myri10ge/myri10ge.c:1939:22: note: 'cmd.data2' was declared here
>  1939 |  struct myri10ge_cmd cmd;
> 
> It would be nice to understand how to make other compilers catch this as
> well, but for the moment I'll just shut up the warning by fixing the
> undefined behavior in this driver.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: initialize two more instances of these [Simon Horman]

Sorry, but looking at this again I found a few more.

diff --git a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
index 4743064bc6d4..feda51e23958 100644
--- a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
+++ b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
@@ -2258,6 +2258,8 @@ static int myri10ge_get_txrx(struct myri10ge_priv *mgp, int slice)
 		    (mgp->sram + cmd.data0);
 	}
 	cmd.data0 = slice;
+	cmd.data1 = 0;
+	cmd.data2 = 0;
 	status |= myri10ge_send_cmd(mgp, MXGEFW_CMD_GET_SMALL_RX_OFFSET,
 				    &cmd, 0);
 	ss->rx_small.lanai = (struct mcp_kreq_ether_recv __iomem *)
@@ -2489,7 +2491,6 @@ static int myri10ge_open(struct net_device *dev)
 static int myri10ge_close(struct net_device *dev)
 {
 	struct myri10ge_priv *mgp = netdev_priv(dev);
-	struct myri10ge_cmd cmd;
 	int status, old_down_cnt;
 	int i;
 
@@ -2508,8 +2509,13 @@ static int myri10ge_close(struct net_device *dev)
 
 	netif_tx_stop_all_queues(dev);
 	if (mgp->rebooted == 0) {
+		struct myri10ge_cmd cmd;
+
 		old_down_cnt = mgp->down_cnt;
 		mb();
+	        cmd.data0 = 0;
+		cmd.data1 = 0;
+		cmd.data2 = 0;
 		status =
 		    myri10ge_send_cmd(mgp, MXGEFW_CMD_ETHERNET_DOWN, &cmd, 0);
 		if (status)

Even with this, I'm sure there are cases
where stale values are passed in cases like this.
But that seems out of scope for this patch.

  /* setup cmd.data* */
  myri10ge_send_cmd(...);
  /* Something else */
  myri10ge_send_cmd(..);