Re: [RFC][PATCH] scripts with stdin replaced

allbery@kf8nh.apk.net
Mon, 5 Jul 1999 13:05:47 -0400 (EDT)

On 5 Jul, Richard Guenther wrote:
+-----
| On Mon, 5 Jul 1999, Jamie Lokier wrote:
| > - Open fd 3, pass /proc/self/fd/3 as the script name.
|
| And rewrite each program to _not_ open("/proc/self/fd/3") as
| this is just a symlink to the real file, i.e. I could have passed
| the filename right away.
+--->8

bzzzt. It's not really a symlink; it's just made to look like one so
e.g . ls on /proc/*/fd behaves semi-sanely. (Remember, /proc isn't a
normal filesystem.)

You can't apply normal symlink-replacement attacks against
/proc/self/fd/*: the only way to alter or replace those is to modify
the process's in-kernel file table. It is therefore a safe way to pass
the script.

-- 
brandon s. allbery	[os/2][linux][solaris][japh]	 allbery@kf8nh.apk.net
system administrator	     [WAY too many hats]	   allbery@ece.cmu.edu
carnegie mellon / electrical and computer engineering			 KF8NH
     We are Linux. Resistance is an indication that you missed the point.




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