netdev - Re: Bluetooth fixes for 2.6.20-rc4

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Message-Id: <20070107.172411.132927338.davem@davemloft.net>
Date:	Sun, 07 Jan 2007 17:24:11 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	marcel@...tmann.org
Cc:	netdev@...r.kernel.org
Subject: Re: Bluetooth fixes for 2.6.20-rc4

From: Marcel Holtmann <marcel@...tmann.org>
Date: Mon, 08 Jan 2007 02:19:13 +0100

> Hi Dave,
> 
> > > Commit: 2b2e64be763c5e64d4ae4a061825b18decf1edf7 
> > > Author: Marcel Holtmann <marcel@...tmann.org> Mon, 08 Jan 2007 01:00:33 +0100 
> > > 
> > >     [Bluetooth] Fix uninitialized return value for RFCOMM sendmsg()
> > >     
> > >     When calling send() with a zero length parameter on a RFCOMM socket
> > >     it returns a positive value. In this rare case the variable err is
> > >     used uninitialized and unfortunately its value is returned.
> > >     
> > >     Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
> > 
> > You can't fix this bug like that.
> > 
> > If sendmsg() sends any bytes, it should return the number of
> > bytes sent even if an error occurs mid-stream.
> > 
> > With this change, you'll now return the error instead of
> > the number of bytes sent.  That's what the new "sent = err"
> > assignment does.
> > 
> > You have to do sendmsg() with those semantics, or else you lose
> > information in that the user can never know how many bytes were
> > actually sent successfully.  Losing the error after successfully sent
> > bytes is OK, if the error persists the user will get it when it
> > recalls sendmsg() to push the rest of the remaining bytes out.
> > 
> > The original code tried to do it right.
> > 
> > If the bug is that 'err' is uninitialized, why try to fix this
> > by being fancy, just initialize it :-)
> 
> We have "int sent = 0" and exactly that is returned if "len == 0".

Marcel, please reread my email, then you can hit reply again ok :)

You broke the case where len != 0, you're going to return an error
code when "sent != 0" and that's a bug, sendmsg() must return the
number of bytes sent if non-zero even if an error occurs.
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