Re: [PATCH 1/2] audit: add support for the openat2 syscall

[Christian Brauner <christian.brauner@ubuntu.com>]

On Thu, Mar 18, 2021 at 11:48:45AM +0100, Christian Brauner wrote:
> [+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.)

And one more comment, why return a hard-coded integer from all of these
architectures instead of introducing an enum in a central place with
proper names idk:

enum audit_match_perm_t {
	.
	.
	.
	AUDIT_MATCH_PERM_EXECVE = 5,
	AUDIT_MATCH_PERM_OPENAT2 = 6,
	.
	.
	.
}

Then you can drop these hard-coded comments too and it's way less
brittle overall.

Christian