Forwarding to LSM-ML again. Any comments? On 2020/06/24 15:39, Alexei Starovoitov wrote: > On Wed, Jun 24, 2020 at 01:58:33PM +0900, Tetsuo Handa wrote: >> On 2020/06/24 13:00, Alexei Starovoitov wrote: >>>> However, regarding usermode_blob, although the byte array (which contains code / data) >>>> might be initially loaded from the kernel space (which is protected), that byte array >>>> is no longer protected (e.g. SIGKILL, strace()) when executed because they are placed >>>> in the user address space. Thus, LSM modules (including pathname based security) want >>>> to control how that byte array can behave. >>> >>> It's privileged memory regardless. root can poke into kernel or any process memory. >> >> LSM is there to restrict processes running as "root". > > hmm. do you really mean that it's possible for an LSM to restrict CAP_SYS_ADMIN effectively? > LSM can certainly provide extra level of foolproof-ness against accidental > mistakes, but it's not a security boundary. > >> Your "root can poke into kernel or any process memory." response is out of step with the times. >> >> Initial byte array used for usermode blob might be protected because of "part of .rodata or >> .init.rodata of kernel module", but that byte array after started in userspace is no longer >> protected. >> >> I don't trust such byte array as "part of kernel module", and I'm asking you how >> such byte array does not interfere (or be interfered by) the rest of the system. > > Could you please explain the attack vector that you see in such scenario? > How elf binaries embedded in the kernel modules different from pid 1? > If anything can peek into their memory the system is compromised. > Say, there are no user blobs in kernel modules. How pid 1 memory is different > from all the JITed images? How is it different for all memory regions shared > between kernel and user processes? > I see an opportunity for an LSM to provide a protection against non-security > bugs when system is running trusted apps, but not when arbitrary code can > execute under root. >
