Re: [PATCH] fs: make generic_block_fiemap sig-tolerant PING2...

[Dmitry Monakhov <dmonakhov@openvz.org>]

[-- Attachment #1.1: Type: text/plain, Size: 1052 bytes --]

Andrew Morton <akpm@linux-foundation.org> writes:

> On Wed, 10 Dec 2014 16:49:18 +0300 Dmitry Monakhov <dmonakhov@openvz.org> wrote:
>
>> 
>> Hello. Someone please take care of this patch.
>> 
>> W/o that patch unprivileged user may abuse system resources simply by spawning
>> wast number of unkilable busyloops (works on ext2/ext3):
>> 
>> truncate --size 1T test
>> for ((i=0;i<1024;i++))
>> do
>>        filefrag test > /dev/null &
>> done
>> 
>> >> --- a/fs/ioctl.c
>> >> +++ b/fs/ioctl.c
>> >> @@ -379,6 +379,11 @@ int __generic_block_fiemap(struct inode *inode,
>> >>  				past_eof = true;
>> >>  		}
>> >>  		cond_resched();
>> >> +		if (fatal_signal_pending(current)) {
>> >> +			ret = -EINTR;
>> >> +			break;
>> >> +		}
>> >> +
>> >>  	} while (1);
>> >>  
>
> Is FIEMAP documented anywhere (manpage)?  If so, that will need an
> update.
Yes you right. I just thought that it is assumed by default.
The only place I know is Documentation/filesystems/fiemap.txt
Please fold patch attached to original one.

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 472 bytes --]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: 0001-doc-fimemap-update-signal-behaviour.patch --]
[-- Type: text/x-diff, Size: 936 bytes --]

>From f7af425b2ac920065491a478b4f4359f422b3453 Mon Sep 17 00:00:00 2001
From: Dmitry Monakhov <dmonakhov@openvz.org>
Date: Fri, 19 Dec 2014 13:11:29 +0400
Subject: [PATCH] doc: fimemap update signal behaviour


Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 Documentation/filesystems/fiemap.txt |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/Documentation/filesystems/fiemap.txt b/Documentation/filesystems/fiemap.txt
index 1b805a0..f6d9c99 100644
--- a/Documentation/filesystems/fiemap.txt
+++ b/Documentation/filesystems/fiemap.txt
@@ -196,7 +196,8 @@ struct fiemap_extent_info {
 };
 
 It is intended that the file system should not need to access any of this
-structure directly.
+structure directly. Filesystem handlers should be tolerant to signals and return
+EINTR once fatal signal received.
 
 
 Flag checking should be done at the beginning of the ->fiemap callback via the
-- 
1.7.1