1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
|
[[!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
|
