From: ebiederm@xmission.com (Eric W. Biederman) To: Eric Paris <eparis@parisplace.org> Cc: Amerigo Wang <amwang@redhat.com>, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, eparis@redhat.com Subject: Re: [Patch] kexec_load: check CAP_SYS_MODULE Date: Fri, 07 Jan 2011 12:10:44 -0800 [thread overview] Message-ID: <m1k4igjwzf.fsf@fess.ebiederm.org> (raw) In-Reply-To: <AANLkTinLhAuSny735kofonAkaqwJvjjDHMUed_r03rVc@mail.gmail.com> (Eric Paris's message of "Thu, 6 Jan 2011 14:02:47 -0500") Eric Paris <eparis@parisplace.org> writes: > On Thu, Jan 6, 2011 at 3:47 AM, Eric W. Biederman <ebiederm@xmission.com> wrote: >> Amerigo Wang <amwang@redhat.com> writes: >> >>> Eric pointed out that kexec_load() actually allows you to >>> run any code you want in ring0, this is more like CAP_SYS_MODULE. >> >> Let me get this straight you want to make the permission checks >> less stringent by allowing either CAP_SYS_MODULE or CAP_SYS_BOOT? > > Nope, read my patch again. It actually requires BOTH of them. Ah right. Testing the negative and going to -EPERM. >> 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. 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. Eric
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From: ebiederm@xmission.com (Eric W. Biederman) To: Eric Paris <eparis@parisplace.org> Cc: kexec@lists.infradead.org, Amerigo Wang <amwang@redhat.com>, eparis@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [Patch] kexec_load: check CAP_SYS_MODULE Date: Fri, 07 Jan 2011 12:10:44 -0800 [thread overview] Message-ID: <m1k4igjwzf.fsf@fess.ebiederm.org> (raw) In-Reply-To: <AANLkTinLhAuSny735kofonAkaqwJvjjDHMUed_r03rVc@mail.gmail.com> (Eric Paris's message of "Thu, 6 Jan 2011 14:02:47 -0500") Eric Paris <eparis@parisplace.org> writes: > On Thu, Jan 6, 2011 at 3:47 AM, Eric W. Biederman <ebiederm@xmission.com> wrote: >> Amerigo Wang <amwang@redhat.com> writes: >> >>> Eric pointed out that kexec_load() actually allows you to >>> run any code you want in ring0, this is more like CAP_SYS_MODULE. >> >> Let me get this straight you want to make the permission checks >> less stringent by allowing either CAP_SYS_MODULE or CAP_SYS_BOOT? > > Nope, read my patch again. It actually requires BOTH of them. Ah right. Testing the negative and going to -EPERM. >> 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. 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. Eric _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
next prev parent reply other threads:[~2011-01-07 20:10 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 [this message] 2011-01-07 20:10 ` Eric W. Biederman 2011-01-07 20:32 ` Eric Paris 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
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