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linux-imx/Documentation/sysctl
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Willy Tarreau 2a032e307d pipe: limit the per-user amount of pages allocated in pipes 
commit 759c01142a upstream.

On no-so-small systems, it is possible for a single process to cause an
OOM condition by filling large pipes with data that are never read. A
typical process filling 4000 pipes with 1 MB of data will use 4 GB of
memory. On small systems it may be tricky to set the pipe max size to
prevent this from happening.

This patch makes it possible to enforce a per-user soft limit above
which new pipes will be limited to a single page, effectively limiting
them to 4 kB each, as well as a hard limit above which no new pipes may
be created for this user. This has the effect of protecting the system
against memory abuse without hurting other users, and still allowing
pipes to work correctly though with less data at once.

The limit are controlled by two new sysctls : pipe-user-pages-soft, and
pipe-user-pages-hard. Both may be disabled by setting them to zero. The
default soft limit allows the default number of FDs per process (1024)
to create pipes of the default size (64kB), thus reaching a limit of 64MB
before starting to create only smaller pipes. With 256 processes limited
to 1024 FDs each, this results in 1024*64kB + (256*1024 - 1024) * 4kB =
1084 MB of memory allocated for a user. The hard limit is disabled by
default to avoid breaking existing applications that make intensive use
of pipes (eg: for splicing).

Reported-by: socketpair@gmail.com
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Mitigates: CVE-2013-4312 (Linux 2.0+)
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
2016-04-21 13:11:54 +02:00
..
00-INDEX sysctl: remove obsolete comments 2011-01-13 08:03:18 -08:00
abi.txt Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
fs.txt pipe: limit the per-user amount of pages allocated in pipes 2016-04-21 13:11:54 +02:00
kernel.txt vsprintf: check real user/group id for %pK 2013-12-04 11:05:12 -08:00
net.txt qdisc: allow setting default queuing discipline 2013-08-31 00:32:32 -04:00
README Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sunrpc.txt Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
vm.txt mm, pcp: allow restoring percpu_pagelist_fraction default 2014-07-18 15:51:01 +02:00

README

Documentation for /proc/sys/ kernel version 2.2.10 (c) 1998, 1999, Rik van Riel riel@nl.linux.org

'Why', I hear you ask, 'would anyone even want documentation for them sysctl files? If anybody really needs it, it's all in the source...'

Well, this documentation is written because some people either don't know they need to tweak something, or because they don't have the time or knowledge to read the source code.

Furthermore, the programmers who built sysctl have built it to be actually used, not just for the fun of programming it :-)

==============================================================

Legal blurb:

As usual, there are two main things to consider:

  1. you get what you pay for
  2. it's free

The consequences are that I won't guarantee the correctness of this document, and if you come to me complaining about how you screwed up your system because of wrong documentation, I won't feel sorry for you. I might even laugh at you...

But of course, if you do manage to screw up your system using only the sysctl options used in this file, I'd like to hear of it. Not only to have a great laugh, but also to make sure that you're the last RTFMing person to screw up.

In short, e-mail your suggestions, corrections and / or horror stories to: riel@nl.linux.org

Rik van Riel.

==============================================================

Introduction:

Sysctl is a means of configuring certain aspects of the kernel at run-time, and the /proc/sys/ directory is there so that you don't even need special tools to do it! In fact, there are only four things needed to use these config facilities:

  • a running Linux system
  • root access
  • common sense (this is especially hard to come by these days)
  • knowledge of what all those values mean

As a quick 'ls /proc/sys' will show, the directory consists of several (arch-dependent?) subdirs. Each subdir is mainly about one part of the kernel, so you can do configuration on a piece by piece basis, or just some 'thematic frobbing'.

The subdirs are about: abi/ execution domains & personalities debug/ dev/ device specific information (eg dev/cdrom/info) fs/ specific filesystems filehandle, inode, dentry and quota tuning binfmt_misc <Documentation/binfmt_misc.txt> kernel/ global kernel info / tuning miscellaneous stuff net/ networking stuff, for documentation look in: <Documentation/networking/> proc/ sunrpc/ SUN Remote Procedure Call (NFS) vm/ memory management tuning buffer and cache management

These are the subdirs I have on my system. There might be more or other subdirs in another setup. If you see another dir, I'd really like to hear about it :-)