Miscellaneous
IRC, #hurd, around September 2010
<youpi> jkoenig: from a quick read, your procfs implementation seems quite
simple, probably much more what I was expecting from Madhusudan (who
probably now hates you :) )
<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).