Miscellaneous

IRC, #hurd, around September 2010

<youpi> jkoenig: is it not possible to provide a /proc/self which points at
  the client's pid?
<pinotree> (also, shouldn't /proc/version say something else than "Linux"?)
<youpi> to make linux tools work, no :/
<youpi> kfreebsd does that too
<pinotree> really?
<youpi> yes
<youpi> (kfreebsd, not freebsd)
<pinotree> does kbsd's one print just "Linux version x.y.z" too, or
  something more eg in a second line?
<pinotree> (as curiosity)
<youpi> % cat /proc/version
<youpi> Linux version 2.6.16 (des@freebsd.org) (gcc version 4.3.5) #4 Sun
  Dec 18 04:30:00 CET 1977
<pinotree> k
<giselher> I had some problems with killall5 to read the pid from /proc, Is
  this now more reliable?
<youpi> I haven't tested with jkoenig's implementation
[...]
<pinotree> looks like he did 'self' too, see rootdir_entries[] in rootdir.c
<youpi> but it doesn't point at self
<antrik> youpi: there is no way to provide /proc/self, because the server
  doesn't know the identity of the client
<youpi> :/
<antrik> youpi: using the existing mechanisms, we would need another magic
  lookup type
<antrik> an alternative idea I discussed with cfhammer once would be for
  the client to voluntarily provide it's identity to the server... but that
  would be a rather fundamental change that requires careful consideration
<antrik> also, object migration could be used, so the implementation would
  be provided by the server, but the execution would happen in the
  client... but that's even more involved :-)
<youpi> but we've seen how much that'd help with a lot of other stuff
<antrik> I'm not sure whether we discussed this on the ML at some point, or
  only on IRC
<youpi> it "just" needs to be commited :)
<antrik> in either case, it can't hurt to bring this up again :-)

root group

IRC, #hurd, around October 2010

<pinotree> the only glitch is that files/dirs have the right user as
  owner, but always with root group

/proc/[PID]/stat being 400 and not 444, and some more

IRC, freenode, #hurd, 2011-03-27

<pochu> is there a reason for /proc/$pid/stat to be 400 and not 444 like on
  Linux?
<pochu> there is an option to procfs to make it 444 like Linux
<pochu> jkoenig: ^
<jkoenig> pochu, hi
<jkoenig> /proc/$pid/stat reveals information which is not usually
  available on Hurd
<jkoenig> so I made it 400 by default to avoid leaking anything
<pochu> is there a security risk in providing that info?
<jkoenig> probably not so much, but it seemed like it's not really a
  descision procfs should make
<jkoenig> I'm not sure which information we're speaking about, though, I
  just remember the abstract reason.
<pochu> things like the pid, the memory, the priority, the state...
<pochu> sounds safe to expose
<jkoenig> also it's 0444 by default in "compatible" mode
<jkoenig> (which is necessary for the linux tools to work well)
<pochu> yeah I saw that :)
<pochu> my question is, should we change it to 0444 by default? if there
  are no security risks and this improves compatibility, sounds like a good
  thing to me
<pochu> we're already 'leaking' part of that info through e.g. ps
<jkoenig> I think /proc should be translated by /hurd/procfs --compatible
  by default (I'm not sure whether it's already the case)
<jkoenig> also I'm not sure why hurd-ps is setuid root, rather than the
  proc server being less paranoid, but maybe I'm missing something.
<pochu> jkoenig: it's not, at least not on Debian
<pochu> youpi: hi, what do you think about starting procfs with
  --compatible by default?
<pochu> youpi: or changing /proc/$pid/stat to 0444 like on Linux
  (--compatible does that among a few other things)
<youpi> I guess you need it for something?
<pochu> I'm porting libgtop :)
<youpi> k
<pochu> though I still think we should do this in procfs itself
<youpi> ymmv
<jkoenig> pochu, youpi, --compatible is also needed because mach's high
  reported sysconf(_SC_CLK_TCK) makes some integers overflow (IIRC)
<youpi> agreed
<jkoenig> luckily, tools which use procfs usually try to detect the value
  /proc uses rather than rely on CLK_TCK
<jkoenig> (so we can choose whatever reasonable value we want)

IRC, freenode, #hurd, 2011-03-28

<antrik> jkoenig: does procfs expose any information that is not available
  to everyone through the proc server?...
<antrik> also, why is --compatible not the default; or rather, why is there
  even another mode? the whole point of procfs is compatibility...
<jkoenig> antrik, yes, through the <pid>/environ and (as mentionned above)
  <pid>/stat files, but I've been careful to make these files readable only
  to the process owner
<jkoenig> --compatible is not the default because it relaxes this paranoia
  wrt. the stat file, and does not conform to the specification with regard
  to clock tick counters
<antrik> what specification?
<jkoenig> the linux proc(5) manpage
<jkoenig> which says clock tick counters are in units of
  1/sysconf(_SC_CLK_TCK)
<antrik> so you are saying that there is some information that the Hurd
  proc server doesn't expose to unprivileged processes, but linux /proc
  does?
<jkoenig> yes
<antrik> that's odd. I wonder what the reasoning behind that could be
<antrik> but this information is available through Hurd ps?
<antrik> BTW, what exactly is _SC_CLK_TCK supposed to be?
<pinotree> jkoenig: hm, just tried with two random processes on linux
  (2.6.32), and enrivon is 400
<pinotree> (which makes sense, as you could have sensible informations eg
  in http_proxy or other envvars)
<jkoenig> antrik, CLK_TCK is similar to HZ (maybe clock resolution instead
  of time slices ?)
<jkoenig> sysconf(3) says "The number of clock ticks per second."
<jkoenig> antrik, I don't remember precisely what information this was, but
  ps-hurd is setuid root.
<jkoenig> anyway, if you run procfs --compatible as a user and try to read
  foo/1/stat, the result is an I/O error, which is the result of the proc
  server denying access.
<antrik> but Linux /proc acutally uses HZ as the unit IIRC? or is
  _SC_CLK_TCK=HZ on Linux?...
<jkoenig> I expect they're equal.
<jkoenig> in practice procps uses heuristics to guess what value /proc uses
  (for compatibility purposes with older kernels)
<jkoenig> I don't think HZ is POSIX, while _SC_CLK_TCK is specifies as the
  unit for (at least) the values returned by times()
<jkoenig> s/specifies/specified/
<jkoenig> antrik, some the information is fetched directly from mach by
  libps, and understandably, the proc server does not give the task port to
  anyone who asks.
<antrik> well, as long as the information is exposed through ps, there is
  no point in hiding it in procfs...
<antrik> and I'm aware of the crazy guessing in libproc... I was actually
  mentoring the previous procfs implementation
<antrik> (though I never got around to look at his buggy code...)
<jkoenig> ok

IRC, freenode, #hurd, 2011-07-22

<pinotree> hm, why /proc/$pid/stat is 600 instead of 644 of linux?
<jkoenig> pinotree, it reveals information which, while not that sensitive,
  would not be available to users through the normal proc interface.
<jkoenig> (it's available through the ps command which is setuid root)
<jkoenig> we discussed at some point making it 644, IIRC.
<pinotree> hm, then why is it not a problem on eg linux?
<jkoenig> (btw you can change it with the -s option.)
<jkoenig> pinotree, it's not a problem because the information is not that
  sensitive, but when rewriting procfs I preferred to play it self and
  consider it's not procfs' job to decide what is sensitive or not.
<jkoenig> IIRC it's not sensitive but you need the task port to query it.
<jkoenig> like, thread times or something.
<pinotree> status is 644 though
<jkoenig> but status contains information which anyone can ask to the proc
  server anyway, I think.

/proc/mounts, /proc/[PID]/mounts

IRC, freenode, #hurd, 2011-07-25

< pinotree> jkoenig: btw, what do you think about providing empty
  /proc/mounts and /proc/$pid/mounts files?
< jkoenig> pinotree, I guess one would have to evaluate the consequences
  wrt. existing use cases (in other words, "I have absolutely no clue
  whatsoever about whether that would be desirable" :-)
< jkoenig> pinotree, the thing is, an error message like "/proc/mounts: No
  such file or directory" is rather explicit, whereas errors which would be
  caused by missing data in /proc/mounts would maybe be harder to track
< braunr> this seems reasonable though
< braunr> there already are many servers with e.g. grsecurity or chrooted
  environments where mounts is empty
< pinotree> well, currently we also have an empty mtab
< braunr> pinotree: but what do you need that for ?
< braunr> pinotree: the init system ?
< pinotree> and the mnt C api already returns no entries (or it bails out,
  i don't remember)
< pinotree> not a strict need

/proc/[PID]/auxv, /proc/[PID]/exe, /proc/[PID]/mem

Needed by glibc's pldd tool (commit 11988f8f9656042c3dfd9002ac85dff33173b9bd).

/proc/self/exe

id:"alpine.LFD.2.02.1110111111260.2016@akari". Needed by glibc's stdlib/tst-secure-getenv.c.

Is it generally possible to use something like the following instead? Disadvantage is that every program using this needs to be patched.

#include <dlfcn.h>
[...]
Dl_info DLInfo;
int err = dladdr(&main, &DLInfo);
if (err == 0)
  [...]
/* Pathname of shared object that contains address: DLInfo.dli_fname.  */
/* Filter it through realpath.  */

This is used in [LLVM]/lib/Support/Unix/Path.inc.

/proc/[PID]/fd/

IRC, freenode, #hurd, 2012-04-24

<antrik> braunr: /proc/*/fd can be implemented in several ways. none of
  them would require undue centralisation
<antrik> braunr: the easiest would be adding one more type of magic lookup
  to the existing magic lookup mechanism
<antrik> wait, I mean /proc/self... for /proc/*/fd it's even more
  straighforward -- we might even have a magic lookup for that already
<pinotree> i guess the ideal thing would be implement that fd logic in
  libps
<antrik> pinotree: nope. it doesn't need to ask proc (or any other server)
  at all. it's local information. that's what we have the magic lookups for
<antrik> one option we were considering at some point would be using the
  object migration mechanism, so the actual handling would still happen
  client-side, but the server could supply the code doing it. this would
  allow servers to add arbitrary magic lookup methods without any global
  modifications... but has other downsides :-)
<gnu_srs> youpi: How much info for /proc/*/fd is possible to get from
  libps? Re: d-h@
<youpi> see my mail
<youpi> I don't think there is an interface for that
<youpi> processes handle fds themselves
<youpi> so libps would have to peek in there
<youpi> and I don't remember having seen any code like that
<gnu_srs> 10:17:17< antrik> wait, I mean /proc/self... for /proc/*/fd it's
  even more straighforward -- we might even have a magic lookup for that
  already
<gnu_srs> pinotree: For me that does not ring a bell on RPCs. Don't know
  what magic means,,
<youpi> for /proc/self/fd we have a magic lookup
<youpi> for /proc/pid/fd, I don't think we have
<gnu_srs> magic lookup*
<gnu_srs> magic lookup == RPC?
<youpi> magic lookup is a kind of answer to the lookup RPC
<youpi> that basically says "it's somewhere else, see there"
<youpi> the magic FD lookup tells the process "it's your FD number x"
<youpi> which works for /proc/self/fd, but not /proc/pid/fd
<civodul> youpi, gnu_srs: regarding FDs, there the msg_get_fd RPC that
  could be used
<civodul> `msgport' should have --get-fd, actually
<youpi> civodul: I assumed that the reason why msgport doesn't have it is
  that it didn't exist
<youpi> so we can get a port on the fd
<youpi> but then how to know what it is?
<civodul> youpi: ah, you mean for the /proc/X/fd symlinks?
<civodul> good question
<civodul> it's not designed to be mapped back to names, indeed :-)
<antrik> youpi: yeah, I realized myself that only /proc/self/fd is trivial
<antrik> BTW, in Linux it's nor real symlinks. it's magic, with some very
  strange (but useful in certain situations) semantics
<antrik> not real symlinks
<antrik> it's very weird for example for fd connected to files that have
  been unlinked. it looks like a broken symlink, but when dereferencing
  (e.g. with cp), you get the actual file contents...

/proc/[PID]/maps

GNU Savannah bug #32770

IRC, OFTC, #debian-hurd, 2012-06-20

<pinotree> bdefreese: the two elfutils tests fail because there are no
  /proc/$pid/maps files
<pinotree> that code is quite relying on linux features, like locating the
  linux kernel executables and their modules, etc
<pinotree> (see eg libdwfl/linux-kernel-modules.c)
<pinotree> refactor elfutils to have the linux parts executed only on linux
  :D
<bdefreese> Oh yeah, the maintainer already seems really thrilled about
  Hurd..  Did you see
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=662041 ?
<pinotree> kurt is generally helpful with us (= hurd)
<pinotree> most probably there he is complaining that we let elfutils build
  with nocheck (ie skipping the test suite run) instead of investigate and
  report why the test suite failed

/proc/[PID]/cwd

IRC, freenode, #hurd, 2012-06-30

* pinotree has a local work to add the /proc/$pid/cwd symlink, but relying
    on "internal" (but exported) glibc functions

"Unusual" PIDs

Not actually related to procfs, but here seems to be a convenient place for filing these:

IRC, freenode, #hurd, 2012-08-10

<braunr> too bad the proc server has pid 0
<braunr> top & co won't show it

IRC, OFTC, #debian-hurd, 2012-09-18

<pinotree> youpi: did you see
  https://enc.com.au/2012/09/careful-with-pids/'
<pinotree> ?
<youpi> nope

CPU Usage

IRC, freenode, #hurd, 2013-01-30

<gnu_srs> Hi, htop seems to report CPU usage correct, but not top, is that
  a known issue? 
<youpi> does your /proc have the -c flag?
<gnu_srs> /hurd/procfs -c
<youpi> I don't remember which way it works, but iirc depending on whether
  -c is there or not, it will work or not
<youpi> problem being that nothing says linux' clock is 100Hz, but a lot of
  programs assume it
<gnu_srs> seems like htop gets it right though
<youpi> possibly just by luc
<youpi> k

IRC, freenode, #hurd, 2013-01-31

<braunr> both htop and top seem to have problems report the cpu time
<braunr> so i expect the problem to be in procfs