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Wed, 06 Apr 2022 19:36:16 -0700 (PDT) Received: from localhost ([193.203.214.57]) by smtp.gmail.com with ESMTPSA id a9-20020ac85b89000000b002e2072c9dedsm15758392qta.67.2022.04.06.19.36.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Apr 2022 19:36:15 -0700 (PDT) Message-ID: <624e4e1f.1c69fb81.7e74e.f971@mx.google.com> X-Google-Original-Message-ID: <20220407023612.GA2490044@cgel.zte@gmail.com> Date: Thu, 7 Apr 2022 02:36:12 +0000 From: CGEL To: Richard Guy Briggs Subject: Re: [PATCH] audit: do a quick exit when syscall number is invalid References: <20220326094654.2361956-1-yang.yang29@zte.com.cn> <62465bf3.1c69fb81.d5424.365e@mx.google.com> <2777189.mvXUDI8C0e@x2> <624803f7.1c69fb81.972da.2dd0@mx.google.com> <624cea8e.1c69fb81.422be.e03b@mx.google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; 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charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, Apr 06, 2022 at 12:49:54PM -0400, Richard Guy Briggs wrote: > On 2022-04-06 01:19, CGEL wrote: > > 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 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 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. > > Going back to the very first quoted line above, if you can generate a > test case that shows that audit is missing an auditable event, that is a > bug that should be fixed. > To reproduce "missing auditing invalid syscall": 1.add audit rule auditctl -a always,exit -F arch=b64 -S all 2.run program with invalid syscalls Code as below. Both syscall can not be audited. #include #include #include #include #include #include #include #include #include #include int main(int argc, char * argv[]) { int syscall_num = -1; syscall(syscall_num, 0, NULL); printf("syscall num is %d errno is %d, %s, %d\n",syscall_num, errno, __FILE__, __LINE__); syscall_num = 3000; syscall(syscall_num, 0, NULL); printf("syscall num is %d errno is %d, %s, %d\n",syscall_num, errno, __FILE__, __LINE__); return 1; } > > > > > > > > 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 > > - RGB > > -- > Richard Guy Briggs > Sr. S/W Engineer, Kernel Security, Base Operating Systems > Remote, Ottawa, Red Hat Canada > IRC: rgb, SunRaycer > Voice: +1.647.777.2635, Internal: (81) 32635 -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit