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Date:   Thu, 18 Mar 2021 11:48:43 +0100
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Richard Guy Briggs <rgb@redhat.com>
Cc:     Linux-Audit Mailing List <linux-audit@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Paul Moore <paul@paul-moore.com>,
        Eric Paris <eparis@parisplace.org>,
        Steve Grubb <sgrubb@redhat.com>, x86@kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Eric Paris <eparis@redhat.com>, linux-alpha@vger.kernel.org,
        linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
        sparclinux@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Aleksa Sarai <cyphar@cyphar.com>
Subject: Re: [PATCH 1/2] audit: add support for the openat2 syscall
Message-ID: <20210318104843.uiga6tmmhn5wfhbs@wittgenstein>
References: <cover.1616031035.git.rgb@redhat.com>
 <49510cacfb5fbbaa312a4a389f3a6619675007ab.1616031035.git.rgb@redhat.com>
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[+Cc Aleksa, the author of openat2()]

and a comment below. :)

On Wed, Mar 17, 2021 at 09:47:17PM -0400, Richard Guy Briggs wrote:
> The openat2(2) syscall was added in kernel v5.6 with commit fddb5d430ad9
> ("open: introduce openat2(2) syscall")
> 
> Add the openat2(2) syscall to the audit syscall classifier.
> 
> See the github issue
> https://github.com/linux-audit/audit-kernel/issues/67
> 
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
>  arch/alpha/kernel/audit.c          | 2 ++
>  arch/ia64/kernel/audit.c           | 2 ++
>  arch/parisc/kernel/audit.c         | 2 ++
>  arch/parisc/kernel/compat_audit.c  | 2 ++
>  arch/powerpc/kernel/audit.c        | 2 ++
>  arch/powerpc/kernel/compat_audit.c | 2 ++
>  arch/s390/kernel/audit.c           | 2 ++
>  arch/s390/kernel/compat_audit.c    | 2 ++
>  arch/sparc/kernel/audit.c          | 2 ++
>  arch/sparc/kernel/compat_audit.c   | 2 ++
>  arch/x86/ia32/audit.c              | 2 ++
>  arch/x86/kernel/audit_64.c         | 2 ++
>  kernel/auditsc.c                   | 3 +++
>  lib/audit.c                        | 4 ++++
>  lib/compat_audit.c                 | 4 ++++
>  15 files changed, 35 insertions(+)
> 
> diff --git a/arch/alpha/kernel/audit.c b/arch/alpha/kernel/audit.c
> index 96a9d18ff4c4..06a911b685d1 100644
> --- a/arch/alpha/kernel/audit.c
> +++ b/arch/alpha/kernel/audit.c
> @@ -42,6 +42,8 @@ int audit_classify_syscall(int abi, unsigned syscall)
>  		return 3;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/arch/ia64/kernel/audit.c b/arch/ia64/kernel/audit.c
> index 5192ca899fe6..5eaa888c8fd3 100644
> --- a/arch/ia64/kernel/audit.c
> +++ b/arch/ia64/kernel/audit.c
> @@ -43,6 +43,8 @@ int audit_classify_syscall(int abi, unsigned syscall)
>  		return 3;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/arch/parisc/kernel/audit.c b/arch/parisc/kernel/audit.c
> index 9eb47b2225d2..fc721a7727ba 100644
> --- a/arch/parisc/kernel/audit.c
> +++ b/arch/parisc/kernel/audit.c
> @@ -52,6 +52,8 @@ int audit_classify_syscall(int abi, unsigned syscall)
>  		return 3;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/arch/parisc/kernel/compat_audit.c b/arch/parisc/kernel/compat_audit.c
> index 20c39c9d86a9..fc6d35918c44 100644
> --- a/arch/parisc/kernel/compat_audit.c
> +++ b/arch/parisc/kernel/compat_audit.c
> @@ -35,6 +35,8 @@ int parisc32_classify_syscall(unsigned syscall)
>  		return 3;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 1;
>  	}
> diff --git a/arch/powerpc/kernel/audit.c b/arch/powerpc/kernel/audit.c
> index a2dddd7f3d09..8f32700b0baa 100644
> --- a/arch/powerpc/kernel/audit.c
> +++ b/arch/powerpc/kernel/audit.c
> @@ -54,6 +54,8 @@ int audit_classify_syscall(int abi, unsigned syscall)
>  		return 4;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/arch/powerpc/kernel/compat_audit.c b/arch/powerpc/kernel/compat_audit.c
> index 55c6ccda0a85..ebe45534b1c9 100644
> --- a/arch/powerpc/kernel/compat_audit.c
> +++ b/arch/powerpc/kernel/compat_audit.c
> @@ -38,6 +38,8 @@ int ppc32_classify_syscall(unsigned syscall)
>  		return 4;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 1;
>  	}
> diff --git a/arch/s390/kernel/audit.c b/arch/s390/kernel/audit.c
> index d395c6c9944c..d964cb94cfaf 100644
> --- a/arch/s390/kernel/audit.c
> +++ b/arch/s390/kernel/audit.c
> @@ -54,6 +54,8 @@ int audit_classify_syscall(int abi, unsigned syscall)
>  		return 4;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/arch/s390/kernel/compat_audit.c b/arch/s390/kernel/compat_audit.c
> index 444fb1f66944..f7b32933ce0e 100644
> --- a/arch/s390/kernel/compat_audit.c
> +++ b/arch/s390/kernel/compat_audit.c
> @@ -39,6 +39,8 @@ int s390_classify_syscall(unsigned syscall)
>  		return 4;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 1;
>  	}
> diff --git a/arch/sparc/kernel/audit.c b/arch/sparc/kernel/audit.c
> index a6e91bf34d48..b6dcca9c6520 100644
> --- a/arch/sparc/kernel/audit.c
> +++ b/arch/sparc/kernel/audit.c
> @@ -55,6 +55,8 @@ int audit_classify_syscall(int abi, unsigned int syscall)
>  		return 4;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/arch/sparc/kernel/compat_audit.c b/arch/sparc/kernel/compat_audit.c
> index 10eeb4f15b20..d2652a1083ad 100644
> --- a/arch/sparc/kernel/compat_audit.c
> +++ b/arch/sparc/kernel/compat_audit.c
> @@ -39,6 +39,8 @@ int sparc32_classify_syscall(unsigned int syscall)
>  		return 4;
>  	case __NR_execve:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 1;
>  	}
> diff --git a/arch/x86/ia32/audit.c b/arch/x86/ia32/audit.c
> index 6efe6cb3768a..57a02ade5503 100644
> --- a/arch/x86/ia32/audit.c
> +++ b/arch/x86/ia32/audit.c
> @@ -39,6 +39,8 @@ int ia32_classify_syscall(unsigned syscall)
>  	case __NR_execve:
>  	case __NR_execveat:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 1;
>  	}
> diff --git a/arch/x86/kernel/audit_64.c b/arch/x86/kernel/audit_64.c
> index 83d9cad4e68b..39de1e021258 100644
> --- a/arch/x86/kernel/audit_64.c
> +++ b/arch/x86/kernel/audit_64.c
> @@ -53,6 +53,8 @@ int audit_classify_syscall(int abi, unsigned syscall)
>  	case __NR_execve:
>  	case __NR_execveat:
>  		return 5;
> +	case __NR_openat2:
> +		return 6;
>  	default:
>  		return 0;
>  	}
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 8bb9ac84d2fb..f5616e70d129 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -76,6 +76,7 @@
>  #include <linux/fsnotify_backend.h>
>  #include <uapi/linux/limits.h>
>  #include <uapi/linux/netfilter/nf_tables.h>
> +#include <uapi/linux/openat2.h>
>  
>  #include "audit.h"
>  
> @@ -195,6 +196,8 @@ static int audit_match_perm(struct audit_context *ctx, int mask)
>  		return ((mask & AUDIT_PERM_WRITE) && ctx->argv[0] == SYS_BIND);
>  	case 5: /* execve */
>  		return mask & AUDIT_PERM_EXEC;
> +	case 6: /* openat2 */
> +		return mask & ACC_MODE((u32)((struct open_how *)ctx->argv[2])->flags);

That looks a bit dodgy. Maybe sm like the below would be a bit better?

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 47fb48f42c93..531e882a5096 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -159,6 +159,7 @@ static const struct audit_nfcfgop_tab audit_nfcfgs[] = {

 static int audit_match_perm(struct audit_context *ctx, int mask)
 {
+       struct open_how *openat2;
        unsigned n;
        if (unlikely(!ctx))
                return 0;
@@ -195,6 +196,12 @@ static int audit_match_perm(struct audit_context *ctx, int mask)
                return ((mask & AUDIT_PERM_WRITE) && ctx->argv[0] == SYS_BIND);
        case 5: /* execve */
                return mask & AUDIT_PERM_EXEC;
+       case 6: /* openat2 */
+               openat2 = ctx->argv[2];
+               if (upper_32_bits(openat2->flags))
+                       pr_warn("Some sensible warning about unknown flags");
+
+               return mask & ACC_MODE(lower_32_bits(openat2->flags));
        default:
                return 0;
        }

(Ideally we'd probably notice at build-time that we've got flags
exceeding 32bits. Could probably easily been done by exposing an all
flags macro somewhere and then we can place a BUILD_BUG_ON() or sm into
such places.)

Christian