Re: [PATCH] trace: events: cleanup deprecated strncpy uses

[Chuck Lever]

On Mon, Apr 01, 2024 at 11:48:52PM +0000, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> For 2 out of 3 of these changes we can simply swap in strscpy() as it
> guarantess NUL-termination which is needed for the following trace
> print.
> 
> trace_rpcgss_context() should use memcpy as its format specifier %.*s
> allows for the length to be specifier (__entry->len). Due to this,
> acceptor does not technically need to be NUL-terminated. Moreover,
> swapping in strscpy() and keeping everything else the same could result
> in truncation of the source string by one byte. To remedy this, we could
> use `len + 1` but I am unsure of the size of the destination buffer so a
> simple memcpy should suffice.
> |	TP_printk("win_size=%u expiry=%lu now=%lu timeout=%u acceptor=%.*s",
> |		__entry->window_size, __entry->expiry, __entry->now,
> |		__entry->timeout, __entry->len, __get_str(acceptor))
> 
> I suspect acceptor not to naturally be a NUL-terminated string due to
> the presence of some stringify methods.
> |	.crstringify_acceptor	= gss_stringify_acceptor,
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  include/trace/events/mdio.h   | 2 +-
>  include/trace/events/rpcgss.h | 2 +-
>  include/trace/events/sock.h   | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/trace/events/mdio.h b/include/trace/events/mdio.h
> index 0f241cbe00ab..285b3e4f83ba 100644
> --- a/include/trace/events/mdio.h
> +++ b/include/trace/events/mdio.h
> @@ -25,7 +25,7 @@ TRACE_EVENT_CONDITION(mdio_access,
>  	),
>  
>  	TP_fast_assign(
> -		strncpy(__entry->busid, bus->id, MII_BUS_ID_SIZE);
> +		strscpy(__entry->busid, bus->id, MII_BUS_ID_SIZE);
>  		__entry->read = read;
>  		__entry->addr = addr;
>  		__entry->regnum = regnum;
> diff --git a/include/trace/events/rpcgss.h b/include/trace/events/rpcgss.h
> index ba2d96a1bc2f..274c297f1b15 100644
> --- a/include/trace/events/rpcgss.h
> +++ b/include/trace/events/rpcgss.h
> @@ -618,7 +618,7 @@ TRACE_EVENT(rpcgss_context,
>  		__entry->timeout = timeout;
>  		__entry->window_size = window_size;
>  		__entry->len = len;
> -		strncpy(__get_str(acceptor), data, len);
> +		memcpy(__get_str(acceptor), data, len);
>  	),
>  
>  	TP_printk("win_size=%u expiry=%lu now=%lu timeout=%u acceptor=%.*s",
> diff --git a/include/trace/events/sock.h b/include/trace/events/sock.h
> index fd206a6ab5b8..1d0b98e6b2cc 100644
> --- a/include/trace/events/sock.h
> +++ b/include/trace/events/sock.h
> @@ -109,7 +109,7 @@ TRACE_EVENT(sock_exceed_buf_limit,
>  	),
>  
>  	TP_fast_assign(
> -		strncpy(__entry->name, prot->name, 32);
> +		strscpy(__entry->name, prot->name, 32);
>  		__entry->sysctl_mem[0] = READ_ONCE(prot->sysctl_mem[0]);
>  		__entry->sysctl_mem[1] = READ_ONCE(prot->sysctl_mem[1]);
>  		__entry->sysctl_mem[2] = READ_ONCE(prot->sysctl_mem[2]);
> 
> ---
> base-commit: 928a87efa42302a23bb9554be081a28058495f22
> change-id: 20240401-strncpy-include-trace-events-mdio-h-0a325676b468
> 
> Best regards,
> --
> Justin Stitt <justinstitt@xxxxxxxxxx>
> 

Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx>


-- 
Chuck Lever