linux-kernel - Re: [RESEND] [PATCH] VFS: make file->f

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]

Message-ID: <20081009235158.7d328aa0@diego-desktop>
Date:	Thu, 9 Oct 2008 23:51:58 +0200
From:	dcg <diegocalleja@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit
 arch

El Wed, 08 Oct 2008 08:51:51 +0200, Peter Zijlstra <a.p.zijlstra@...llo.nl> escribió:

> either dup() the fd or open() the file twice. There is absolutely no
> valid reason to have two threads read from the same fd without
> synchronising their access to it - never.

In case this is the final consensus, I think that a topic that is brought
to the list every few months and even generates (aparently not neccesary)
patches is a hint that there should be somewhere a commentary (*) like
this:

(*) I don't know if what I wrote is 100% correct.


Signed-off-by: Diego Calleja García <diegocg@...il.com>

Index: 2.6/include/linux/fs.h
===================================================================
--- 2.6.orig/include/linux/fs.h	2008-10-09 00:06:50.000000000 +0200
+++ 2.6/include/linux/fs.h	2008-10-09 00:29:03.000000000 +0200
@@ -821,6 +821,18 @@
 	atomic_long_t		f_count;
 	unsigned int 		f_flags;
 	mode_t			f_mode;
+	/*
+	 * Linux does NOT guarantee atomic reading/writing to file->f_pos in
+	 * multithread apps running in 32 bit machines. There're several
+	 * reasons for this behaviour:
+	 *  - Specifications don't say it must be implemented that way.
+	 *  - This behaviour is part of the Linux semantics.
+	 *  - Any application that does multithreaded access to file->f_pos
+	 *    should be doing its own locking: the processes should synchronize
+	 *    themselves when accessing a file descriptor. If an application
+	 *    doesn't do that, its file descriptor handling is buggy anyway and
+	 *    must be fixed to access file->f_pos properly.
+	 */
 	loff_t			f_pos;
 	struct fown_struct	f_owner;
 	unsigned int		f_uid, f_gid;

--
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/