linux-kernel - Re: [RFC PATCH 1/2] VFS: Kill use of O

lists.openwall.net		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 linux-hardening linux-cve-announce 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:	Tue, 22 Sep 2015 17:12:42 +0100
From:	David Howells <dhowells@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	dhowells@...hat.com, viro@...iv.linux.org.uk,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	xfs@....sgi.com
Subject: Re: [RFC PATCH 1/2] VFS: Kill use of O_LARGEFILE inside the kernel

Theodore Ts'o <tytso@....edu> wrote:

> So what this means is that on 32-bit systems, if we have a userspace
> program which isn't using the Largefile-enabled, and it opens a file
> which is larger than can be addressed with a 32-bit off_t, it can get
> surprised and possibly cause data loss.

Good point.  I was initially thinking that 32-bit userspace on a 64-bit system
would have O_LARGEFILE automatically enabled - but I guess it'll trap through
the compat entry points which avoid that.

That said, fanotify and xfs_open_by_handle() will both automatically set
O_LARGEFILE irrespectively of the 32-bitness of the original caller.

Further, path-based truncate() makes no checks based on file-largeness, unlike
ftruncate().

> Is this something we are willing to live with?  After all, there was a
> originally a really good reason for the O_LARGEFILE flag in the first
> place, and it was primarily about making sure that a non-LARGEFILE
> capable program would hard fail on the open, instead of after it had
> trashed the user's data.

Okay, that seems reasonable - but it still leaves truncate() dangling.  I'm
not sure there's a good answer to that, though.

> Was there a reason that motivated this change, other than just an
> clean up?

Overlayfs and one or two other places need to potentially apply O_LARGEFILE to
the things that they do on behalf of userspace - but other than suppressing
some size checks, it seems to be ignored by the filesystems and the VM.

I vaguely seem to remember that at one point there were still filesystems that
couldn't handle large files and would reject such opens - but they appear to
all have been fixed.

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/