Messages in this thread |  | | | Subject | Re: [RFC v2 00/10] snet: Security for NETwork syscalls | | From | Tetsuo Handa <> | | Date | Sun, 7 Mar 2010 14:45:20 +0900 |
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Hello.
Samir Bellabes wrote: > Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> writes: > > > Regarding [RFC v2 09/10] snet: introduce snet_ticket > > +enum snet_verdict snet_ticket_check(struct snet_info *info) > > +{ > > + struct snet_ticket *st = NULL; > > + unsigned int h = 0, verdict = SNET_VERDICT_NONE; > > + struct list_head *l = NULL; > > + struct snet_task_security *tsec = NULL; > > + > > + if (snet_ticket_mode == SNET_TICKET_OFF) > > + goto out; > > + > > + tsec = (struct snet_task_security*) current_security(); > > + > > + h = jhash_2words(info->syscall, info->protocol, 0) % HSIZE; > > + l = &tsec->hash[h]; > > + > > + read_lock_bh(&tsec->lock); > > > > Credentials are allocated for copy-on-write basis. > > Sharing "tsec" among multiple "struct task_struct" is what you intended? > > No, there is no shared "tsec". > snet_ticket_check() is called from the process context. So "tsec" is > a pointer to the "void *security" pointer from its own "struct > task_struct". > Until 2.6.28:
"void *security" is directory attached to "struct task_struct". copy_process() calls security_task_alloc().
Therefore, task1->security != task2->security is guaranteed as long as you do
task->security = kmalloc();
at security_task_alloc().
Since 2.6.29:
"void *security" is attached to "struct cred", and "struct cred *" is attached to "struct task_struct". copy_process() calls copy_creds() and prepare_creds() calls security_prepare_creds(). But copy_creds() does not call prepare_creds() for clone(CLONE_THREAD) case.
Therefore, task1->cred->security != task2->cred->security is not guaranteed even if you do
cred->security = kmalloc();
at security_prepare_creds().
> every task_struct have a "tsec" allocated to its "void *security" > pointer.
You meant to have assigned "void *security" dedicated to "struct task_struct". But "void *security" is no longer directly attached to "struct task_struct". I couldn't find code that checks whether "current->cred" is used by only current thread or not. "current->cred" being used by only current thread is a requirement for having a "tsec" allocated to every "struct task_struct".
Your code will share "tsec" among multiple threads if a process created threads using clone(CLONE_THREAD | CLONE_SIGHAND | CLONE_VM). Each thread has its own "struct task_struct" but they share "cred->security". Sharing "tsec" among multiple threads is what you intended?
Regards.
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