From: Eric Paris <eparis@redhat.com> To: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Amerigo Wang <amwang@redhat.com>, linux-kernel@vger.kernel.org, kexec@lists.infradead.org Subject: Re: [Patch] kexec_load: check CAP_SYS_MODULE Date: Fri, 07 Jan 2011 15:32:13 -0500 [thread overview] Message-ID: <1294432333.3237.107.camel@localhost.localdomain> (raw) In-Reply-To: <m1k4igjwzf.fsf@fess.ebiederm.org> On Fri, 2011-01-07 at 12:10 -0800, Eric W. Biederman wrote: > Eric Paris <eparis@parisplace.org> writes: > >> CAP_SYS_BOOT is the correct capability. Sure you can run any > >> code but only after rebooting. I don't see how this differs > >> from any other reboot scenario. > > > > The difference is that after a reboot the bootloader and the system > > control what code is run. kexec_load() immediately runs the new > > kernel which is not controlled by the bootloader or by the system. > > Imagine a situation where the bootloader and the /boot directory are > > RO (enforced by hardware). kexec_load() would let you run any kernel > > code you want on the box whereas reboot would not. > > The scenario is imaginable (not common but imaginable) but I don't see > how requiring CAP_SYS_MODULE makes anything better. > > If I was building a configuration where I didn't want anyone to be able > to direct the kernel into a different state by locking down the > bootloaders I expect I would compile out the syscall as well. As sad as it may sound the vast majority of people don't build their own kernels. And even those people who have the intelligence to do it are often constrained by some non-technical policy to run 'approved' kernels. > Most bootloaders have the option of booting something else the mechanism > is just different. I really don't see what the addition of > CAP_SYS_MODULE gains you. > > Right now CAP_SYS_BOOT still makes sense to me and CAP_SYS_MODULE stills > seems like nonsense in this context. There is no question in my mind that CAP_SYS_BOOT makes sense. We are violently agreed on that point. The problem is reboot() != kexec_load() kexec_load() is as close to init_module() as it is to reboot(). Maybe I didn't make it clear how this is going to be used. I plan to drop CAP_SYS_MODULE to stop root from loading their own modules and running their own code in the kernel. I can control reboot() since I control the platform and the bootloader. I cannot control kexec(). I'm also required to use a generic distro kernel (bet you can't guess which one) The only solution I see to solve the problem is to gate kexec on CAP_SYS_MODULE. Which makes sense since kexec() is in many respects close to module_init() than it is to reboot(). -Eric
WARNING: multiple messages have this Message-ID (diff)
From: Eric Paris <eparis@redhat.com> To: "Eric W. Biederman" <ebiederm@xmission.com> Cc: kexec@lists.infradead.org, Amerigo Wang <amwang@redhat.com>, linux-kernel@vger.kernel.org Subject: Re: [Patch] kexec_load: check CAP_SYS_MODULE Date: Fri, 07 Jan 2011 15:32:13 -0500 [thread overview] Message-ID: <1294432333.3237.107.camel@localhost.localdomain> (raw) In-Reply-To: <m1k4igjwzf.fsf@fess.ebiederm.org> On Fri, 2011-01-07 at 12:10 -0800, Eric W. Biederman wrote: > Eric Paris <eparis@parisplace.org> writes: > >> CAP_SYS_BOOT is the correct capability. Sure you can run any > >> code but only after rebooting. I don't see how this differs > >> from any other reboot scenario. > > > > The difference is that after a reboot the bootloader and the system > > control what code is run. kexec_load() immediately runs the new > > kernel which is not controlled by the bootloader or by the system. > > Imagine a situation where the bootloader and the /boot directory are > > RO (enforced by hardware). kexec_load() would let you run any kernel > > code you want on the box whereas reboot would not. > > The scenario is imaginable (not common but imaginable) but I don't see > how requiring CAP_SYS_MODULE makes anything better. > > If I was building a configuration where I didn't want anyone to be able > to direct the kernel into a different state by locking down the > bootloaders I expect I would compile out the syscall as well. As sad as it may sound the vast majority of people don't build their own kernels. And even those people who have the intelligence to do it are often constrained by some non-technical policy to run 'approved' kernels. > Most bootloaders have the option of booting something else the mechanism > is just different. I really don't see what the addition of > CAP_SYS_MODULE gains you. > > Right now CAP_SYS_BOOT still makes sense to me and CAP_SYS_MODULE stills > seems like nonsense in this context. There is no question in my mind that CAP_SYS_BOOT makes sense. We are violently agreed on that point. The problem is reboot() != kexec_load() kexec_load() is as close to init_module() as it is to reboot(). Maybe I didn't make it clear how this is going to be used. I plan to drop CAP_SYS_MODULE to stop root from loading their own modules and running their own code in the kernel. I can control reboot() since I control the platform and the bootloader. I cannot control kexec(). I'm also required to use a generic distro kernel (bet you can't guess which one) The only solution I see to solve the problem is to gate kexec on CAP_SYS_MODULE. Which makes sense since kexec() is in many respects close to module_init() than it is to reboot(). -Eric _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
next prev parent reply other threads:[~2011-01-07 20:32 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-01-06 8:25 [Patch] kexec_load: check CAP_SYS_MODULE Amerigo Wang 2011-01-06 8:25 ` Amerigo Wang 2011-01-06 8:27 ` Cong Wang 2011-01-06 8:27 ` Cong Wang 2011-01-06 8:47 ` Eric W. Biederman 2011-01-06 8:47 ` Eric W. Biederman 2011-01-06 19:02 ` Eric Paris 2011-01-06 19:02 ` Eric Paris 2011-01-07 20:10 ` Eric W. Biederman 2011-01-07 20:10 ` Eric W. Biederman 2011-01-07 20:32 ` Eric Paris [this message] 2011-01-07 20:32 ` Eric Paris 2011-01-07 21:02 ` Eric W. Biederman 2011-01-07 21:02 ` Eric W. Biederman 2011-01-08 0:39 ` Eric Paris 2011-01-08 0:39 ` Eric Paris 2011-01-09 2:09 ` Eric W. Biederman 2011-01-09 2:09 ` Eric W. Biederman 2011-01-11 11:26 ` Cong Wang 2011-01-11 11:26 ` Cong Wang 2011-01-14 19:47 ` Eric Paris 2011-01-14 19:47 ` Eric Paris
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=1294432333.3237.107.camel@localhost.localdomain \ --to=eparis@redhat.com \ --cc=amwang@redhat.com \ --cc=ebiederm@xmission.com \ --cc=kexec@lists.infradead.org \ --cc=linux-kernel@vger.kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.