On 09/29/2013 07:41 PM, George Spelvin wrote: >> Right, so the pppd application is actually doing the correct thing. > And a CAP_SYSLOG setuid binary that *doesn't* DTRT seems like a more > immediate security hole than leaking kernel addresses. After all > kptr_restrict is optional precisely because the benefit is marginal. > > The interesting question is what credentials make sense for %pK outside > of a seq_printf(). Does it even make sense in a generic printk? In that > case, it's the permission of the syslogd that matters rather than the > process generating the message. > >> Will wait and see what others have to say. > Me, too. Dan in particular.
Firstly, I wouldn't recommend applying %pK's to printk usage. Removing all addresses from the kernel syslog compromises its usefulness in debugging basically anything at all. Additionally, many printk calls are performed from a context where a capability check would yield unpredictable (or at least meaningless) results. If you want to restrict access to the kernel syslog by unprivileged users, that should be done by enabling CONFIG_DMESG_RESTRICT, which was written for this purpose. With that out of the way, I don't have a strong opinion on how to handle this case. The proposed patch solves the problem but may break setuid applications that expect to be able to read /proc/kallsyms contents based on euid (and implicitly, capabilities) alone. But then again, these mythical setuid applications are probably broken in some situations anyway, because what happens if /proc/kallsyms is set to "2" (unconditionally replace addresses with 0's)? I also can't think of a better solution. -Dan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
