Messages in this thread |  | | | Date | Sat, 04 Sep 2004 11:06:31 +0200 | | From | Kristian Sørensen <> | | Subject | Re: [Umbrella-devel] Re: Getting full path from dentry in LSM hooks |
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Valdis.Kletnieks@vt.edu wrote: > 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.... I was not precise enough - it is not just fork, but the LSM catches every time a new process is created - so we do have some way of generic catching creation of processes, and denying so, if prohibited.
> 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); You are right! ... as long as a new process is not created, this may do some damage ... but:
> 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, Not mny suid programs would really need to be able to access the /etc and everything below... E.g. cdrecord (there were a bug a year ago or something)... it should definitely not have access to the possiblílities you mention!
> 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. Good point!
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