Re: [PATCH] audit: do a quick exit when syscall number is invalid

On Mon, Apr 04, 2022 at 11:58:50AM -0400, Richard Guy Briggs wrote: > On 2022-04-02 08:06, CGEL wrote: > > On Fri, Apr 01, 2022 at 10:16:45AM -0400, Paul Moore wrote: > > > On Fri, Apr 1, 2022 at 9:39 AM Steve Grubb <sgrubb(a)redhat.com&gt; wrote: > > > > On Thursday, March 31, 2022 9:57:05 PM EDT CGEL wrote: > > > > > On Thu, Mar 31, 2022 at 10:16:23AM -0400, Paul Moore wrote: > > > > > > On Wed, Mar 30, 2022 at 10:29 PM CGEL <cgel.zte(a)gmail.com&gt; wrote: > > > > > > > On Wed, Mar 30, 2022 at 10:48:12AM -0400, Paul Moore wrote: > > > > > > > > If audit is not generating SYSCALL records, even for invalid/ENOSYS > > > > > > > > syscalls, I would consider that a bug which should be fixed. > > > > > > > > > > > > > > If we fix this bug, do you think audit invalid/ENOSYS syscalls better > > > > > > > be forcible or be a rule that can be configure? I think configure is > > > > > > > better. > > > > > > > > > > > > It isn't clear to me exactly what you are asking, but I would expect > > > > > > the existing audit syscall filtering mechanism to work regardless if > > > > > > the syscall is valid or not. > > > > > > > > > > Thanks, I try to make it more clear. We found that auditctl would only > > > > > set rule with syscall number (>=0 && <2047) ... > > > > > > That is exactly why I wrote the warning below in my response ... > > > > > I think the question is more clear now. > > > > 1) libaudit.c wants to forbid setting invalid syscall, but inconsistent > > Currently way(>=0 && <2047) is inconsistent, syscall with number 2000 and > > syscall with number 3000 are both invalid syscall. But 2000 can be set by > > auditctl, and 3000 cannot be set by auditctl. > > A better way to do this forbidden is to use __NR_syscalls(asm-generic/unistd.h). > > > > 2) if libaudit.c do the right forbidden, kernel better ignore invalid syscall > > See this patch. > > > > If we want audit invalid syscall as you said before. libaudit.c should not > > do the forbidden, auditctl should allow setting syscall rule with 'any' number. > > So do you think we should fix libaudit.c? > > I'm having a bit of trouble understanding what you've said above. > > The kernel ultimately must protect itself from malice and mistakes, so > it must verify all data sent to it. > > Userspace can help by knowing what that kernel policy is so it can avoid > violating that policy or provide useful feedback if it can't. Userspace > can be used to make things more efficient, but the kernel is the last > step for security. > > If userspace and the kernel are mismatched or out of sync, then the > kernel enforces policy to protect itself. Much appreciate for your interpretation. Have you get any idea of how to solve the mismatched? From your viewpoint, I think it's better for kernel to not handle syscall of syscall number<0, because it's invaild of all arch, and has no value for attacker to probing for specific syscall numbers.

> > > > > > to the audit syscall filter, which are unfortunately baked into the > > > > > > current design/implementation, which may affect this to some extent. > > > > > > -- > > > paul-moore.com > > - RGB