On Tue, Sep 12, 2023 at 08:00:12AM -0400, Stephen Smalley wrote: > On Tue, Sep 12, 2023 at 5:00 AM Alfred Piccioni <alpic@xxxxxxxxxx> wrote: > > > > On Mon, Sep 11, 2023 at 3:49 PM Stephen Smalley > > <stephen.smalley.work@xxxxxxxxx> wrote: > > > > > > On Mon, Sep 11, 2023 at 9:19 AM Stephen Smalley > > > <stephen.smalley.work@xxxxxxxxx> wrote: > > > > > > > > On Fri, Sep 8, 2023 at 6:54 PM kernel test robot <lkp@xxxxxxxxx> wrote: > > > > > > > > > > Hi Alfred, > > > > > > > > > > kernel test robot noticed the following build errors: > > > > > > > > > > [auto build test ERROR on 50a510a78287c15cee644f345ef8bac8977986a7] > > > > > > > > > > url: https://github.com/intel-lab-lkp/linux/commits/Alfred-Piccioni/SELinux-Check-correct-permissions-for-FS_IOC32_/20230906-200131 > > > > > base: 50a510a78287c15cee644f345ef8bac8977986a7 > > > > > patch link: https://lore.kernel.org/r/20230906115928.3749928-1-alpic%40google.com > > > > > patch subject: [PATCH V2] SELinux: Check correct permissions for FS_IOC32_* > > > > > config: i386-debian-10.3 (https://download.01.org/0day-ci/archive/20230909/202309090600.NSyo7d2q-lkp@xxxxxxxxx/config) > > > > > compiler: gcc-12 (Debian 12.2.0-14) 12.2.0 > > > > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230909/202309090600.NSyo7d2q-lkp@xxxxxxxxx/reproduce) > > > > > > > > > > If you fix the issue in a separate patch/commit (i.e. not just a new version of > > > > > the same patch/commit), kindly add following tags > > > > > | Reported-by: kernel test robot <lkp@xxxxxxxxx> > > > > > | Closes: https://lore.kernel.org/oe-kbuild-all/202309090600.NSyo7d2q-lkp@xxxxxxxxx/ > > > > > > > > > > All errors (new ones prefixed by >>): > > > > > > > > > > security/selinux/hooks.c: In function 'selinux_file_ioctl': > > > > > >> security/selinux/hooks.c:3647:9: error: duplicate case value > > > > > 3647 | case FS_IOC32_GETFLAGS: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3645:9: note: previously used here > > > > > 3645 | case FS_IOC_GETFLAGS: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3648:9: error: duplicate case value > > > > > 3648 | case FS_IOC32_GETVERSION: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3646:9: note: previously used here > > > > > 3646 | case FS_IOC_GETVERSION: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3654:9: error: duplicate case value > > > > > 3654 | case FS_IOC32_SETFLAGS: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3652:9: note: previously used here > > > > > 3652 | case FS_IOC_SETFLAGS: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3655:9: error: duplicate case value > > > > > 3655 | case FS_IOC32_SETVERSION: > > > > > | ^~~~ > > > > > security/selinux/hooks.c:3653:9: note: previously used here > > > > > 3653 | case FS_IOC_SETVERSION: > > > > > | ^~~~ > > > > > > > > Not sure of the right way to fix this while addressing the original > > > > issue that this patch was intended to fix. Looking in fs/ioctl.c, I > > > > see that the some FS_IOC32 values are remapped to the corresponding > > > > FS_IOC values by the compat ioctl syscall entrypoint. Also notice this > > > > comment there: > > > > > > > > /* RED-PEN how should LSM module know it's handling 32bit? */ > > > > error = security_file_ioctl(f.file, cmd, arg); > > > > if (error) > > > > goto out; > > > > > > > > So perhaps this is a defect in LSM that needs to be addressed? > > > > > > Note btw that some of the 32-bit ioctl commands are only handled in > > > the fs-specific compat_ioctl routines, e.g. ext4_compat_ioctl() > > > handles EXT4_IOC32_GETVERSION == FS_IOC32_GETVERSION and ditto for > > > _SETVERSION. > > > > > > > > > > > > > > > > > > > > > > > > > > vim +3647 security/selinux/hooks.c > > > > > > > > > > 3634 > > > > > 3635 static int selinux_file_ioctl(struct file *file, unsigned int cmd, > > > > > 3636 unsigned long arg) > > > > > 3637 { > > > > > 3638 const struct cred *cred = current_cred(); > > > > > 3639 int error = 0; > > > > > 3640 > > > > > 3641 switch (cmd) { > > > > > 3642 case FIONREAD: > > > > > 3643 case FIBMAP: > > > > > 3644 case FIGETBSZ: > > > > > 3645 case FS_IOC_GETFLAGS: > > > > > 3646 case FS_IOC_GETVERSION: > > > > > > 3647 case FS_IOC32_GETFLAGS: > > > > > 3648 case FS_IOC32_GETVERSION: > > > > > 3649 error = file_has_perm(cred, file, FILE__GETATTR); > > > > > 3650 break; > > > > > 3651 > > > > > 3652 case FS_IOC_SETFLAGS: > > > > > 3653 case FS_IOC_SETVERSION: > > > > > 3654 case FS_IOC32_SETFLAGS: > > > > > 3655 case FS_IOC32_SETVERSION: > > > > > 3656 error = file_has_perm(cred, file, FILE__SETATTR); > > > > > 3657 break; > > > > > 3658 > > > > > 3659 /* sys_ioctl() checks */ > > > > > 3660 case FIONBIO: > > > > > 3661 case FIOASYNC: > > > > > 3662 error = file_has_perm(cred, file, 0); > > > > > 3663 break; > > > > > 3664 > > > > > 3665 case KDSKBENT: > > > > > 3666 case KDSKBSENT: > > > > > 3667 error = cred_has_capability(cred, CAP_SYS_TTY_CONFIG, > > > > > 3668 CAP_OPT_NONE, true); > > > > > 3669 break; > > > > > 3670 > > > > > 3671 case FIOCLEX: > > > > > 3672 case FIONCLEX: > > > > > 3673 if (!selinux_policycap_ioctl_skip_cloexec()) > > > > > 3674 error = ioctl_has_perm(cred, file, FILE__IOCTL, (u16) cmd); > > > > > 3675 break; > > > > > 3676 > > > > > 3677 /* default case assumes that the command will go > > > > > 3678 * to the file's ioctl() function. > > > > > 3679 */ > > > > > 3680 default: > > > > > 3681 error = ioctl_has_perm(cred, file, FILE__IOCTL, (u16) cmd); > > > > > 3682 } > > > > > 3683 return error; > > > > > 3684 } > > > > > 3685 > > > > Hey Stephen, > > > > Thanks for looking into it a bit deeper! This seems a bit of a pickle. > > I can think of a few somewhat hacky ways to fix this. > > > > I can just set the flags to check `if FS_IOC32_*; set FS_IOC_*;`, > > which is the quickest but kinda hacky. > > > > I can go with the other plan of dropping the irrelevant bytes from the > > cmd code, so all codes will be read as u16. This effectively does the > > same thing, but may be unclear. > > > > I can also look into whether this can be solved at the LSM or a higher > > level. Perhaps the filesystems setting `if FS_IOC32_*; set FS_IOC_*;` > > is a hint that something else interesting is going wrong. > > > > I'll spend a little time thinking and investigating and get back with > > a more concrete solution. I'll also need to do a bit more robust > > testing; it built on my machine! > > Likewise for me; I don't generally try building for 32-bit systems. > Remapping FS_IOC32_* to FS_IOC_* in selinux_file_ioctl() seems > reasonable to me although optimally that would be conditional on > whether selinux_file_ioctl() is being called from the compat ioctl > syscall (e.g. adding a flag to the LSM hook to indicate this or using > a separate hook for it). Otherwise we might misinterpret some other > ioctl on 64-bit. I think adding a boolean argument to the LSM hook makes sense. LSMs might decide to handle it or not, at their own pace. > > If we didn't have compatibility requirements, it would be tempting to > just get rid of all the special case ioctl command handling in > selinux_file_ioctl() and let ioctl_has_perm() handle them all with the > extended ioctl permissions support. But that would require a SELinux > policy cap to switch it on conditionally for compatibility at least > and not sure anyone is willing to refactor their policies accordingly.
