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Date:   Sat, 7 Jul 2018 10:13:47 +0200
From:   Samuel Thibault <samuel.thibault@ens-lyon.org>
To:     Jann Horn <jannh@google.com>
Cc:     William Hubbs <w.d.hubbs@gmail.com>,
        Chris Brannon <chris@the-brannons.com>,
        Kirk Reiser <kirk@reisers.ca>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, speakup@linux-speakup.org,
        devel@driverdev.osuosl.org
Subject: Re: [PATCH] staging: speakup: fix wraparound in uaccess length check
Message-ID: <20180707081347.czde44j6rjepjpkf@var.youpi.perso.aquilenet.fr>
Mail-Followup-To: Samuel Thibault <samuel.thibault@ens-lyon.org>,
        Jann Horn <jannh@google.com>, William Hubbs <w.d.hubbs@gmail.com>,
        Chris Brannon <chris@the-brannons.com>,
        Kirk Reiser <kirk@reisers.ca>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, speakup@linux-speakup.org,
        devel@driverdev.osuosl.org
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Jann Horn, le sam. 07 juil. 2018 03:53:44 +0200, a ecrit:
> @@ -257,6 +257,8 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
>  				0x80 | (ch & 0x3f)
>  			};
>  
> +			if (chars_sent + 2 > count)
> +				break;
>  			if (copy_to_user(cp, s, sizeof(s)))
>  				return -EFAULT;

Err, but then we have lost 'ch' that was consumed by the
synth_buffer_getc() call, so the fix seems wrong to me.

Nacked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

Samuel