info for discussion of syscall getdents() kern/117010

[Roman Divacky]

can someone from our ports team comment on this? it would be really nice
to get this fixed... and if the solution is so trivial as providing a
newer version of glibc I am all for it.


On Fri, Feb 29, 2008 at 07:47:31AM -0500, Gary Stanley wrote:
> At 03:36 AM 2/25/2008, sam wrote:
> >hi all
> >
> >links to similar problems:
> >http://mail-index.netbsd.org/current-users/2005/11/13/0011.html
> >
> >>  bug (+fix) in getdents + readdir
> >>  o We're not sure what the Linux kernel intended to place in this field,
> >>    but our experience shows that on "real" file systems (that actually
> >>    reside on some disk) the offset seems to be a simple (not necessarily
> >>    continuous) counter: e.g. first entry may have d_off=1, second: 
> >d_off=2,
> >>    third: d_off=4096, fourth=d_off=4097 etc. We conjecture this is the
> >>    serial of the dirent record within the directory (and so, this is 
> >indeed
> >>    the "offset", but counted in records out of which some were already
> >>    removed).
> >
> >
> >> - In such an "overflow" situation, getdents() tries to lseek (the
> >>  directory-fd) to the end of the last-legal-dirent that getdents()
> >>  has successfully read.
> >>  This offset is supposedly held by the local variable `last_offset'.
> >>  But, since `last_offset' is assigned with `d_off' on each iteration,
> >>  and since as mentioned above `d_off' usually holds an incorrect value,
> >>  the lseek is not performed to the correct place.
> >>  getdents() then returns the number of bytes successfully read.
> I
> I believe I have fixed this problem. I used a newer glibc version, 
> extracted it via cpio/rpm2cpio and it fixes it. It seems the version 
> of glibc that is installed with the fc6 port might have some 
> regression issues, I don't have a free machine to test my theory out. 
> I don't track the glibc changes, so it's rather difficult to say. 
> However, I think this change might have something to do with 
> (fixing?) the issue: 
> http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/unix/sysv/linux/getdents.c.diff?r1=1.22&r2=1.23&cvsroot=glibc
> 
> [root at swamp /usr/servers]# pkg_info|grep linux
> linux_base-fc6-6_5  Base set of packages needed in Linux mode (for 
> i386/amd64)
> 
> bash-3.1# uname -a
> Linux swamp 2.6.16 FreeBSD 7.0-STABLE #2: Fri Feb 29 02:42:04 CST 
> 2008 i686 i686 i386 GNU/Linux
> 
> bash-3.1# ./hlds_run -game cstrike +ip localhost -port 29999 +exec 
> server.cfg +map de_dust2
> Auto detecting CPU
> Using Pentium II Optimised binary.
> Auto-restarting the server on crash
> 
> Console initialized.
> scandir failed:/usr/servers/1.6/./valve/SAVE
> scandir failed:/usr/servers/1.6/./platform/SAVE
> Protocol version 47
> Exe version 1.1.2.5/Stdio (cstrike)
> Exe build: 20:02:49 Oct 24 2006 (3651)
> STEAM Auth Server
> couldn't exec language.cfg
> couldn't exec listip.cfg
> couldn't exec banned.cfg
> Server IP address 127.0.0.1:29999
> scandir failed:/usr/servers/1.6/./valve/SAVE
> scandir failed:/usr/servers/1.6/./platform/SAVE
> net.cpp (926) : Assertion Failed: 0 == iRet
> net.cpp (928) : Assertion Failed: 0 == iRet
> 
> couldn't exec listip.cfg
> couldn't exec banned.cfg
> Adding master server 68.142.72.250:27010
> Adding master server 72.165.61.190:27010
> Connection to Steam servers successful.
> VAC secure mode is activated.
> status
> hostname:  Counter-Strike 1.6 Server
> version :  47/1.1.2.5/Stdio 3651 secure
> tcp/ip  :  127.0.0.1:29999
> map     :  de_dust2 at: 0 x, 0 y, 0 z
> players :  0 active (6 max)
> 
> 
> Anyway, here are some very brief instructions on how i fixed it:
> 
> "cd /compat/linux && fetch 
> ftp://rpmfind.net/linux/fedora/development/x86_64/os/Packages/glibc-2.7.90-7.i386.rpm"
> Then you do a simple "rpm2cpio glibc-2.7.90-7.i386.rpm | cpio -idvu"
> 
> -Gary
> 
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