lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Thu, 07 Aug 2014 15:22:59 +0100
From:	Steven Whitehouse <>
To:	Rob Jones <>,
	"Eric W. Biederman" <>
CC:,,, Al Viro <>,
Subject: Re: [PATCH] seq_file: Allow private data to be supplied
 on seq_open


On 07/08/14 15:16, Rob Jones wrote:
> On 07/08/14 15:09, Rob Jones wrote:
>> Hi Steve,
>> On 07/08/14 14:32, Steven Whitehouse wrote:
>>> Hi,
>>> On 07/08/14 13:58, Rob Jones wrote:
>>> [snip]
>>>> On a related subject, Having looked at a few uses of seq_file, I must
>>>> say that some users seem to make assumptions about the internal
>>>> workings of the module. Dangerous behaviour as only some behaviours 
>>>> are
>>>> documented.
>>>> e.g. The behaviour that "struct seq_file" pointer is stored in
>>>> file->private_data is documented and can therefore be relied upon but
>>>> the fact that the output buffer and its size are only defined at the
>>>> first output (and can therefore be pre-defined and pre-allocated by
>>>> user code) is not documented and could therefore change without 
>>>> warning.
>>>> This second behaviour is assumed in, for example, module 
>>>> fs/gfs2/glock.c
>>>> which could, therefore, stop working properly without warning if the
>>>> internal behaviour was changed.
>>> While it is undocumented, it is I understand, how this feature was
>>> intended to be used, so I think that it is safe to do this in the GFS2
>>> case. Here is a ref to the thread which explains how it landed up like
>>> that:
>> No criticism was intended of that particular piece of code, It has been
>> there for a couple of years and is, presumably, still working :-)
>> It was just a general point about things needing to be written down. A
>> behaviour such as you were relying on can be a very positive thing but
>> it would be of much greater use if it was written down in the file docs.
>> I completely missed seq_file_private() because I was looking at the
> Sorry, that should be seq_open_private()
> Why does one never see the mistake until *after* hitting send?
Always the way, unfortunately!

>> docs more than the code. If it had been written down in the docs it
>> would have saved me quite a bit of time, similarly, if the buffer
>> allocation behaviour was documented, changes to seq_file.c would not be
>> made that could break your code.
>> God knows, I'm not a fan of unnecessary documentation but where it's
>> useful I'm all for it.
Yes, very much agreed, and no doubt it would be useful in this case. I 
hoped that the earlier thread might be a useful starting point, since it 
explained some of the whys and wherefores,


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists