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Full Discussion: Writing to a Serial Port
Top Forums Web Development Writing to a Serial Port Post 302923537 by Corona688 on Monday 3rd of November 2014 01:12:35 PM
Old 11-03-2014
Quote:
Originally Posted by Meow613
Definitely created. If I run the C program as a stand alone, the file is created and I can read it.
I know for a fact that an ordinary webserver cannot and should not write files to /var/www/. That would be a security hole large enough to drop the moon through, with Jupiter and Sirius for change. It's blocked on purpose, to limit the damage a program bug -- or an outright hacking attempt -- can do. When it's blocked, an attacker can't drop malicious programs there even if they try.

It blocks it by running it as a different user. This is why you had to chmod 666 the device file, too. You have access to the device -- the webserver does not. This isn't related to the owner of the program at all, any more than ls would run as root just because root owns it.

There are a few very specific and tightly controlled places your web server is allowed to write, /tmp/ is the main one. Not /temp/, /tmp/. Please give it a try.
 

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CAPTEST:(8)						  System Administration Utilities					       CAPTEST:(8)

NAME
captest - a program to demonstrate capabilities SYNOPSIS
captest [ --drop-all | --drop-caps | --id ] [ --lock ] [ --text ] DESCRIPTION
captest is a program that demonstrates and prints out the current process capabilities. Each option prints the same report. It will output current capabilities. then it will try to access /etc/shadow directly to show if that can be done. Then it creates a child process that attempts to read /etc/shadow and outputs the results of that. Then it outputs the capabilities that a child process would have. You can also apply file system capabilities to this program to study how they work. For example, filecap /usr/bin/captest chown. Then run captest as a normal user. Another interesting test is to make captest suid root so that you can see what the interaction is between root's credentials and capabilities. For example, chmod 4755 /usr/bin/captest. When run as a normal user, the program will see if privilege esca- lation is possible. But do not leave this app setuid root after you are don testing so that an attacker cannot take advantage of it. OPTIONS
--drop-all This drops all capabilities and clears the bounding set. --drop-caps This drops just traditional capabilities. --id This changes to uid and gid 99, drops supplemental groups, and clears the bounding set. --text This option outputs the effective capabilities in text rather than numerically. --lock This prevents the ability for child processes to regain privileges if the uid is 0. SEE ALSO
filecap(8), capabilities(7) AUTHOR
Steve Grubb Red Hat June 2009 CAPTEST:(8)
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