linux-kernel - Re: [PATCH 1/2] nvmet: re-fix tracing strncpy() warning

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Message-Id: <44c39a85-a1e8-4c3f-9416-b1f17e5bc36f@app.fastmail.com>
Date: Fri, 05 Jan 2024 22:40:38 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Keith Busch" <kbusch@...nel.org>
Cc: "Arnd Bergmann" <arnd@...nel.org>, "Christoph Hellwig" <hch@....de>,
 "Sagi Grimberg" <sagi@...mberg.me>, "Chaitanya Kulkarni" <kch@...dia.com>,
 linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
 "Daniel Wagner" <dwagner@...e.de>, "Hannes Reinecke" <hare@...e.de>
Subject: Re: [PATCH 1/2] nvmet: re-fix tracing strncpy() warning

On Fri, Jan 5, 2024, at 21:57, Keith Busch wrote:
> On Fri, Jan 05, 2024 at 09:36:38PM +0100, Arnd Bergmann wrote:
>> On Fri, Jan 5, 2024, at 21:24, Keith Busch wrote:
>> > On Wed, Jan 03, 2024 at 04:56:55PM +0100, Arnd Bergmann wrote:
>> >> @@ -53,8 +53,7 @@ static inline void __assign_req_name(char *name, struct nvmet_req *req)
>> >>  		return;
>> >>  	}
>> >>  
>> >> -	strncpy(name, req->ns->device_path,
>> >> -		min_t(size_t, DISK_NAME_LEN, strlen(req->ns->device_path)));
>> >> +	strscpy_pad(name, req->ns->device_path, DISK_NAME_LEN);
>> >>  }
>> >
>> > I like this one, however Daniel has a different fix for this already
>> > staged in nvme-6.8:
>> >
>> >  
>> > https://git.infradead.org/nvme.git/commitdiff/8f6c0eec5fad13785fd53a5b3b5f8b97b722a2a3
>> 
>> +       snprintf(name,
>> +                min_t(size_t, DISK_NAME_LEN, strlen(req->ns->device_path) + 1),
>> +                "%s", req->ns->device_path);
>> 
>> Don't we still need the zero-padding here to avoid leaking
>> kernel data to userspace?
>
> I'm not sure. This potentially leaves trace buffer memory uninitialized
> after the string, but isn't the trace buffer user accessible when it was
> initially allocated?

I'm always confused by how the tracing macros work exactly, so
I don't know either. Looking through the other tracing headers
with string copies, I see that about half of them use the padding
variants (strncpy or strscpy_pad), while the other half use
non-padding strscpy.

     Arnd