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From: Andrew DeFaria <Andrew AT DeFaria DOT com>
Subject: Re: /proc/*/cmdline corrupted
Date: Sun, 16 Oct 2011 16:59:06 -0700
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References: <CAG_2cT=rmeJpmZbYDo7RAwjNcTTDSTH1SMhuzzL9qi09ZJwGyA AT mail DOT gmail DOT com> <32663265 DOT post AT talk DOT nabble DOT com>
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On 10/16/11 14:31, jan.kolar wrote:
>> jc807j    2668     1  0 08:59 tty0     00:00:00 xterm -e ssh server
> 80x72+285+0 -e ssh server
>> jc807j    3004     1  0 08:59 tty0     00:00:00 xterm -e ssh server
>> 80x72-8+0 -e ssh server
>> jc807j    2928  5852  0 09:12 ?        00:00:00 xterm  20000 +tb
>> The actual command lines for the 3 xterm processes are:
>> C:\cygwin\bin\xterm.exe -sl 20000 +tb -geometry 80x72+285+0 -e ssh server
>> C:\cygwin\bin\xterm.exe -sl 20000 +tb -geometry 80x72-8+0 -e ssh server
>> C:\cygwin\bin\xterm.exe -sl 20000 +tb
> xterm calls XrmParseCommand() that
> "parses an (argc, argv) pair according to the specified option table ... and
> modifies the (argc, argv) pair to remove all recognized options."
>
> Therefore
>           "-sl 20000 +tb -geometry 80x72+285+0"
> is properly removed
> and "-e ssh server" is moved to __argv[1 .. 3].
> Then __argv[4] (respectively __argv[1] for the shorter command) is assigned
> null pointer
> which results in the second "\0" in the od-output below.
>
>
> HOWEVER:
>
> Either XrmParseCommand() does not update argc
> or the change does not propagate (how would that be possible?) to __argc.
> Therefore the command lines appear corrupted this particular way.
>
>
> /proc/*/cmdline  uses a copy of __argc named __argc_safe
> which is hardly to be updated anyway.
> "   for (int i = 0; i<  __argc_safe; i++) "
>
> Funny enough, /proc/self/cmdline is likely to contain shortened version of
> cmdline:
> "     for (char **a = __argv; *a; a++)"
> [ pinfo.cc from cygwin 1.7.9-1 ]
Why wouldn't exec(1) be responsible for setting up /proc and therefore 
fill in cmdline with effectively $0 *before* the program itself ever got 
around to calling XrmParseCommand? (I'm not well versed in the 
underlying mechanics here and I have not reviewed the code but I would 
have thought that something like exec would have examined argv/argc 
before the program was ever able to modify it).
-- 
Andrew DeFaria <http://defaria.com>
Chastity is curable if detected early.


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