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authorThomas Schwinge <thomas@schwinge.name>2011-03-28 10:12:21 +0200
committerThomas Schwinge <thomas@schwinge.name>2011-03-28 10:12:21 +0200
commit1049f72d37aa1efc434c96eff42ad522eb331c90 (patch)
treeb375094668415c1ea28c0233a976bedf9e4e8e5e /hurd/translator/procfs/jkoenig
parent3f5b019c3f6e0c6e1683b2374cc86116251ecf2b (diff)
hurd/translator/procfs/jkoenig/discussion: Place for jkoenig procfs discussion.
Also add recent IRC discussion.
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+[[!meta copyright="Copyright © 2010, 2011 Free Software Foundation, Inc."]]
+
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
+is included in the section entitled [[GNU Free Documentation
+License|/fdl]]."]]"""]]
+
+[[!tag open_issue_hurd]]
+
+[[!toc]]
+
+
+# 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