On Wed, Feb 1, 2012 at 11:02 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Mon, Jan 30, 2012 at 8:17 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> They are normally disallowed because they could be used to subvert >> setuid programs. But if setuid is disabled, then they are safe. >> >> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> --- >> kernel/nsproxy.c | 8 +++++++- >> 1 files changed, 7 insertions(+), 1 deletions(-) >> >> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c >> index b576f7f..47cf873 100644 >> --- a/kernel/nsproxy.c >> +++ b/kernel/nsproxy.c >> @@ -191,7 +191,13 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags, >> CLONE_NEWNET))) >> return 0; >> >> - if (!capable(CAP_SYS_ADMIN)) >> + /* We require either no_new_privs or CAP_SYS_ADMIN for all modes */ >> + if (!current->no_new_privs && !capable(CAP_SYS_ADMIN)) >> + return -EPERM; >> + >> + /* NEWNS and NEWNET always require CAP_SYS_ADMIN. */ >> + if ((unshare_flags & (CLONE_NEWNS | CLONE_NEWNET)) && >> + !capable(CAP_SYS_ADMIN)) >> return -EPERM; >> >> *new_nsp = create_new_namespaces(unshare_flags, current, > > While I think it's unlikely that the list handled by > unshare_nsproxy_namespaces() is going to change, I'd still prefer that > the logic of this test be reversed so that the nnp-allowed flags are > listed instead of the CAP_SYS_ADMIN-required ones so that it will > default to disallowing new flags. It's a little less readable, but > maybe something like this (untested): > > unsigned long handled_mask = (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | > CLONE_NEWNET); > unsigned long npp_mask = (CLONE_NEWUTS | CLONE_NEWIPC); > > if (!(unshare_flags & handled_mask)) > return 0; > > if ( !(current->no_new_privs && > !(unshare_flags & (handled_mask ^ npp_mask))) && > !capable(CAP_SYS_ADMIN)) > return -EPERM; > ... > > This also has the side-effect of removing the double-check of > capable() in some cases. Agreed -- will fix. This patch is also missing the corresponding change for clone. I'll add that. I'm tempted to add CLONE_NEWPID as well (it's _useful_), but there's an unresolved issue with SCM_CREDENTIALS. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
