On 03/25, Ben Woodard wrote: > > Allow threads other than the main thread to do introspection of files in > proc without relying on read permissions. proc_pid_follow_link() calls > proc_fd_access_allowed() which ultimately calls __ptrace_may_access(). > > Though this allows additional access to some proc files, we do not > believe that this has any unintended security implications. However it > probably needs to be looked at carefully. > > The original problem was a thread of a process whose permissions were > 111 couldn't open its own /proc/self/exe This was interfering with a > special purpose debugging tool. A simple reproducer is below.:
To clarify, the test-case fails if the executable is not readable. This is because setup_new_exec()->would_dump() notices that inode_permission(MAY_READ) fails and then we do set_dumpable(suid_dumpable). After that __ptrace_may_access()->get_dumpable() fails. It is not clear why proc_pid_readlink/etc should check get_dumpable(), perhaps we could add PTRACE_MODE_NODUMPABLE. But this is offtopic and I think the patch is fine anyway. > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -234,7 +234,7 @@ static int __ptrace_may_access(struct task_struct > *task, unsigned int mode) > */ > int dumpable = 0; > /* Don't let security modules deny introspection */ > - if (task == current) > + if (same_thread_group(task, current)) > return 0; > rcu_read_lock(); > tcred = __task_cred(task); I agree. I think that any security checks are pointless in this case, both tasks have the same ->mm. Acked-by: Oleg Nesterov <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
