Bug 107887

Summary:	Extra whitespace in comm= field
Product:	dbus	Reporter:	Laurent Bigonville <bigon>
Component:	core	Assignee:	D-Bus Maintainers <dbus>
Status:	RESOLVED MOVED	QA Contact:	D-Bus Maintainers <dbus>
Severity:	minor
Priority:	low
Version:	git master
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:

Description Laurent Bigonville 2018-09-10 13:25:09 UTC

Hi,

It seems that in the log the comm= field contain an extra whitespace at the end:
"dbus-daemon[23494]: [session uid=1000 pid=23494] Connection :1.0 (uid=1000 pid=23495 comm="dbus-monitor " label="unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023") became a monitor."


Looking at the code, it seems that _dbus_command_for_pid() is at fault here. /proc/<pid>/cmdline also contain a final \0 which is translated to a whitespace, this one should probably be stripped?

Comment 1 Simon McVittie 2018-09-10 13:57:48 UTC

Yes, it seems cmdline consists of \0-terminated (rather than \0-separated) words. When translating those into space-separated words for the comm field, the last \0 should be eaten.

% sh -c 'xxd /proc/$$/cmdline'
00000000: 7368 002d 6300 7878 6420 2f70 726f 632f  sh.-c.xxd /proc/
00000010: 2424 2f63 6d64 6c69 6e65 00              $$/cmdline.
% sh -c 'xxd /proc/$$/cmdline' arg0 arg1 "" 
00000000: 7368 002d 6300 7878 6420 2f70 726f 632f  sh.-c.xxd /proc/
00000010: 2424 2f63 6d64 6c69 6e65 0061 7267 3000  $$/cmdline.arg0.
00000020: 6172 6731 0000                           arg1..
          |<----->|
             arg1
                   ->||<-
         empty string between two \0

Comment 2 Simon McVittie 2018-09-10 14:00:19 UTC

Note that /proc/pid/cmdline is trivial to fake (e.g. avahi-daemon edits its own command-line to show status), so comm is just a debug/diagnostic thing, and is not suitable to make part of a security feature.

Comment 3 GitLab Migration User 2018-10-12 21:36:20 UTC

-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

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