jffs2: -ENOSPC when truncating file?!

[Jörn Engel]

On Sun, 24 February 2008 09:36:07 +0900, David Woodhouse wrote:
> On Sun, 2008-02-24 at 00:57 +0100, Pavel Machek wrote:
> > 
> > I'm trying to free space by truncating big file, and I get:
> > 
> > root at fic-gta01:~# ls -al gps.nmea 
> > -rw-r--r--    1 root     root      2332070 Feb 19 22:13 gps.nmea
> > root at fic-gta01:~# > gps.nmea 
> > -sh: cannot create gps.nmea: No space left on device
> > root at fic-gta01:~# rm gps.nmea
> > root at fic-gta01:~# > gps.nmea
> > root at fic-gta01:~# 
> 
> You need to write a log entry indicating the new length of the file.
> There is no space for new log entries.
> 
> There is a special case for removal -- 'rm gps.nmea' would work. Perhaps
> we should add a special case for truncation too, so that it can also use
> the extra pool of free space.

Could a naïve implementation of this get exploited by doing a large
number of truncates that just shave single bytes off various files?

Looks like the safe way to do it would be to write out a replacement
node for the truncated node, if the special case ever triggers.

Jörn

-- 
"[One] doesn't need to know [...] how to cause a headache in order
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-- Scott Culp, Manager of the Microsoft Security Response Center, 2001