net: cxgb4: avoid memcpy beyond end of source buffer

Building with link-time-optimizations revealed that the cxgb4 driver does
a fixed-size memcpy() from a variable-length constant string into the
network interface name:

In function 'memcpy',
    inlined from 'cfg_queues_uld.constprop' at drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.c:335:2,
    inlined from 'cxgb4_register_uld.constprop' at drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.c:719:9:
include/linux/string.h:350:3: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter
   __read_overflow2();
   ^

I can see two equally workable solutions: either we use a strncpy() instead
of the memcpy() to stop at the end of the input, or we make the source buffer
fixed length as well. This implements the latter.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

From: Arnd Bergmann
> Sent: 02 February 2018 15:19
> 
> Building with link-time-optimizations revealed that the cxgb4 driver does
> a fixed-size memcpy() from a variable-length constant string into the
> network interface name:
...
> I can see two equally workable solutions: either we use a strncpy() instead
> of the memcpy() to stop at the end of the input, or we make the source buffer
> fixed length as well. This implements the latter.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.h
> b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.h
> index 1d37672902da..a14e8db51cdc 100644
> --- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.h
> +++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.h
> @@ -355,7 +355,7 @@ struct cxgb4_lld_info {
>  };
> 
>  struct cxgb4_uld_info {
> -	const char *name;
> +	char name[IFNAMSIZ];
>  	void *handle;
>  	unsigned int nrxq;
>  	unsigned int rxq_size;
> --
> 2.9.0

Surely there is another part to this patch?

	David

From: Arnd Bergmann <arnd@arndb.de>
Date: Fri,  2 Feb 2018 16:18:37 +0100

> Building with link-time-optimizations revealed that the cxgb4 driver does
> a fixed-size memcpy() from a variable-length constant string into the
> network interface name:
> 
> In function 'memcpy',
>     inlined from 'cfg_queues_uld.constprop' at drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.c:335:2,
>     inlined from 'cxgb4_register_uld.constprop' at drivers/net/ethernet/chelsio/cxgb4/cxgb4_uld.c:719:9:
> include/linux/string.h:350:3: error: call to '__read_overflow2' declared with attribute error: detected read beyond size of object passed as 2nd parameter
>    __read_overflow2();
>    ^
> 
> I can see two equally workable solutions: either we use a strncpy() instead
> of the memcpy() to stop at the end of the input, or we make the source buffer
> fixed length as well. This implements the latter.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Not the most pleasant thing in the world, but I can't think of a better
solution.

> @@ -355,7 +355,7 @@ struct cxgb4_lld_info {
>  };
>  
>  struct cxgb4_uld_info {
> -	const char *name;
> +	char name[IFNAMSIZ];
>  	void *handle;
>  	unsigned int nrxq;
>  	unsigned int rxq_size;

David Laight asked how this can be the sole part of the patch.

All of these structures are initialized like:

static struct cxgb4_uld_info {
	.name	= "foo",
	...
};

So changing from "const char *" to "char []" just works.