[PATCH net-next] bnx2x: initialize ethtool info->fw_version before use

[PATCH net-next] bnx2x: initialize ethtool info->fw_version before use

[Jonathan Toppins]

If the info->fw_version has garbage in the buffer this can lead to a BUG()
being generated in strlcat() due to the use of strlen(). Initialize the
buffer before use.

The use of a systemtap script can demonstrate the problem by injecting
garbage into fw_version:

    [root@localhost ~]# cat net-info.stp
    //
    // compile and run with command
    //# stap -g   net-info.stp
    //
    probe begin { printf("net-info  version 01.01\n")}

    function memset(msg:long) %{
    	memset((char*)STAP_ARG_msg,-1,196);
    %}

    probe module("bnx2x").function("bnx2x_get_drvinfo")
    {
      printf("In function\n");
      memset(register("rsi"));
    }

    [root@localhost ~]# stap -g net-info.stp &
    net-info  version 01.01
    [root@localhost ~]# ethtool -i eth1

Signed-off-by: Jonathan Toppins <jtoppins@redhat.com>
---
 drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c
index 4a0ba6801c9e..49b906396dcf 100644
--- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c
+++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c
@@ -1111,6 +1111,8 @@ static void bnx2x_get_drvinfo(struct net_device *dev,
 	int ext_dev_info_offset;
 	u32 mbi;
 
+	info->fw_version[0] = 0;
+
 	strlcpy(info->driver, DRV_MODULE_NAME, sizeof(info->driver));
 	strlcpy(info->version, DRV_MODULE_VERSION, sizeof(info->version));
 
-- 
2.16.4

Re: [PATCH net-next] bnx2x: initialize ethtool info->fw_version before use

[Jakub Kicinski]

On Mon, 18 Nov 2019 12:07:53 -0500, Jonathan Toppins wrote:
> If the info->fw_version has garbage in the buffer this can lead to a BUG()
> being generated in strlcat() due to the use of strlen(). Initialize the
> buffer before use.
> 
> The use of a systemtap script can demonstrate the problem by injecting
> garbage into fw_version:


> @@ -1111,6 +1111,8 @@ static void bnx2x_get_drvinfo(struct net_device *dev,
>  	int ext_dev_info_offset;
>  	u32 mbi;
>  
> +	info->fw_version[0] = 0;
> +
>  	strlcpy(info->driver, DRV_MODULE_NAME, sizeof(info->driver));
>  	strlcpy(info->version, DRV_MODULE_VERSION, sizeof(info->version));

I don't know systemtap, so it's very unclear what you're trying to fix
here. Setting random fields of info to 0 seems pointless as the entire
structure is zeroed before the call in ethtool_get_drvinfo().

Please explain.

Re: [PATCH net-next] bnx2x: initialize ethtool info->fw_version before use

[David Miller]

From: Jonathan Toppins <jtoppins@redhat.com>
Date: Mon, 18 Nov 2019 12:07:53 -0500

>     probe begin { printf("net-info  version 01.01\n")}
> 
>     function memset(msg:long) %{
>     	memset((char*)STAP_ARG_msg,-1,196);
>     %}
> 
>     probe module("bnx2x").function("bnx2x_get_drvinfo")
>     {
>       printf("In function\n");
>       memset(register("rsi"));

This makes no sense.

This function is called with the buffer cleared to zero.

You're scrambling something to simulate a "bug", but that will never
be scrambled in reality.