linux-kernel - Re: [PATCH v2] kobject: return -ENOSPC when add_uevent

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Date:   Wed, 19 Jun 2019 19:26:18 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v2] kobject: return -ENOSPC when add_uevent_var() fails

On Tue, Jun 11, 2019 at 06:09:24AM +0900, Masahiro Yamada wrote:
> This function never attempts to allocate memory, so returning -ENOMEM
> looks weird to me. The reason of the failure is there is no more space
> in the given kobj_uevent_env structure.
> 
> Let's change the error code to -ENOSPC.
> 
> This patch is safe since this function had never failed in reality.
> 
> The callers of this function put a fixed number of small strings into
> the buffer.
> 
> The buffer is defined to be large enough:
> 
>   #define UEVENT_NUM_ENVP                 32      /* number of env pointers */
>   #define UEVENT_BUFFER_SIZE              2048    /* buffer for the variables */
> 
> As you see WARN() in the error paths, any failure of this function is
> a software bug.
> 
> If such a case had ever happened before, you would have already seen
> a noisy back-trace, then you would have increased UEVENT_NUM_ENVP or
> UEVENT_BUFFER_SIZE.
> 
> Nobody has ever increased UEVENT_NUM_ENVP or UEVENT_BUFFER_SIZE since
> their addition, that is, this structure is always large enough.

That implies that we should just drop the WARN() entirely.  Especially
given that syzbot runs panic-on-warn, right?

How about doing both things at the same time?

thanks,

greg k-h