Re: [Umbrella-devel] Re: Getting full path from dentry in LSM hooks

[Valdis . Kletnieks]

On Fri, 03 Sep 2004 22:05:03 +0200, =?UTF-8?B?S3Jpc3RpYW4gU8O4cmVuc2Vu?= said:

> Also simple bufferoverflows in suid-root programs may be avoided. The 
> simple way would to set the restriction "no fork", and thus if an 
> attacker tries to fork a (root) shell, this would be denied.

All this does is stop fork().  I'm not sure, but most shellcodes I've seen
don't bother forking, they just execve() a shell....

It doesn't stop a buffer overflow that does this:

	f1 = open("/bin/bash");
	f2 = open("/tmp/bash", O_CREAT);
	while ((bytes = read(f1,buffer,sizeof(buffer))) > 0)
		write(f2,buffer,bytes);
	fchmod(f2,4775);
	close(f1); close(f2);

Papering over *that* one by restricting fchmod just means the exploit needs to
append a line to /etc/passwd, or create a trojan inetd.conf or crontab entry,
or any of the other myriad ways a program can leave a backdoor (there's a
*reason* SELinux ends up with all those rules - this isn't an easy task)...

Remember - just papering over the fact that most shellcodes just execve() a
shell doesn't fix the fundemental problem, which is that the attacker is able
to run code of his choosing as root.

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