linux-kernel - Re: [PATCH] vfs: respect FMODE_UNSIGNED

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Message-ID: <87y51yenlp.fsf@spindle.srvr.nix>
Date:	Wed, 29 Jan 2014 16:53:22 +0000
From:	Nick Alcock <nick.alcock@...cle.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: respect FMODE_UNSIGNED_OFFSET in p(read|write)[v]*().

On 29 Jan 2014, Al Viro outgrape:

> On Wed, Jan 29, 2014 at 11:57:20AM +0000, Nick Alcock wrote:
>>  	ssize_t ret = -EBADF;
>>  
>> -	if (pos < 0)
>> +	f = fdget(fd);
>> +	if ((pos < 0) && (!f.file || !unsigned_offsets(f.file))) {
>> +		fdput(f);
>>  		return -EINVAL;
>> +	}
>
> ... and now pread(-1, ...) fails with EINVAL instead of EBADF.

Sorry, I don't see it. If the fh is invalid, control flow is unchanged
unless pos is also < 0 (that's an && outside the bracketed section, not
an ||, and nothing I've touched changes ret outside that conditional
branch): if pos *is* < 0, we'd have had an EINVAL before and we have one
now, likewise unchanged.

What am I missing?

(Or did you miss the brackets enclosing (!f.file || !unsigned_offsets(f.file))?
If so, I'm not surprised: it would really be easier to read if that
function had the inverse sense, 'signed_offsets()'...)

-- 
NULL && (void)
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