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

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 <redacted>
---
 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);
 	default:
 		return 0;
 	}

diff --git a/lib/audit.c b/lib/audit.c
index 5004bff928a7..8f030b9a2d10 100644
--- a/lib/audit.c
+++ b/lib/audit.c

@@ -60,6 +60,10 @@ int audit_classify_syscall(int abi, unsigned syscall)
 #endif
 	case __NR_execve:
 		return 5;
+#ifdef __NR_openat2
+	case __NR_openat2:
+		return 6;
+#endif
 	default:
 		return 0;
 	}

diff --git a/lib/compat_audit.c b/lib/compat_audit.c
index 77eabad69b4a..8aff0d0d9ba0 100644
--- a/lib/compat_audit.c
+++ b/lib/compat_audit.c

@@ -45,6 +45,10 @@ int audit_classify_compat_syscall(int abi, unsigned syscall)
 #endif
 	case __NR_execve:
 		return 5;
+#ifdef __NR_openat2
+	case __NR_openat2:
+		return 6;
+#endif
 	default:
 		return 1;
 	}

-- 
2.27.0

[+Cc Aleksa, the author of openat2()]

and a comment below. :)

On Wed, Mar 17, 2021 at 09:47:17PM -0400, Richard Guy Briggs wrote:

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

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

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

On 2021-03-18 11:52, Christian Brauner wrote:

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

quoted

On Wed, Mar 17, 2021 at 09:47:17PM -0400, Richard Guy Briggs wrote:

quoted

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 <redacted>

...

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:

Oh, believe me, I tried hard to do that because I really don't like
hard-coded magic values, but for expediency I continued the same
approach until I could sort out the header file mess.  There was an
extra preparatory patch (attached) in this patchset with a different
audit syscall perms patch (also attached).  By including "#include
<linux/audit.h>" in each of the compat source files there were warnings
of redefinitions of every __NR_* syscall number.  The easiest way to get
rid of it would have been to pull the new AUDITSC_* definitions into a
new <linux/auditsc.h> file and include that from <linux/audit.h> and
each of the arch/*/*/*audit.c (and lib/*audit.c) files.

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.

Totally agree.

Christian

- RGB

--
Richard Guy Briggs [off-list ref]
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

On 2021-03-18 11:48, Christian Brauner wrote:

[+Cc Aleksa, the author of openat2()]

Ah!  Thanks for pulling in Aleksa.  I thought I caught everyone...

and a comment below. :)

Same...

On Wed, Mar 17, 2021 at 09:47:17PM -0400, Richard Guy Briggs wrote:

quoted

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 <redacted>
---
 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?

Ah, ok, fair enough, since original flags use a u32 and this was picked
as u64 for alignment.  It was just occurring to me last night that I
might have the dubious honour of being the first usage of 0%llo format
specifier in the kernel...  ;-)

- RGB

--
Richard Guy Briggs [off-list ref]
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

On 2021-03-18 08:08, Richard Guy Briggs wrote:

On 2021-03-18 11:48, Christian Brauner wrote:

quoted

[+Cc Aleksa, the author of openat2()]

Ah!  Thanks for pulling in Aleksa.  I thought I caught everyone...

quoted

and a comment below. :)

Same...

quoted

On Wed, Mar 17, 2021 at 09:47:17PM -0400, Richard Guy Briggs wrote:

quoted

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 <redacted>
---
 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?

Ah, ok, fair enough, since original flags use a u32 and this was picked
as u64 for alignment.  It was just occurring to me last night that I
might have the dubious honour of being the first usage of 0%llo format
specifier in the kernel...  ;-)

quoted

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.)

open_how arguments are translated to open_flags which is limited to 32 bits.

This code is shared with the other open functions that are limited to 32 bits
in open_flags.  openat2 was created to avoid the limitations of openat, so at
some point it isn't unreasonable that flags exceed 32 bits, but open_flags
would have to be modified at that point to accommodate.

This value is handed in from userspace, and could be handed in without being
defined in the kernel, so those values need to be properly checked regardless
of the flags defined in the kernel.

The openat2 syscall claims to check all flags but no check is done on the top
32 bits.

build_open_flags() assigns how->flags to an int, effectively dropping the top
32 bits, before being checked against ~VALID_OPEN_FLAGS.  This happens after
audit mode filtering, but has the same result.

Audit mode filtering using ACC_MODE() already masks out all but the lowest two
bits with O_ACCMODE, so there is no danger of overflowing a u32.

tomoyo_check_open_permission() assigns ACC_MODE() to u8 without a check.

All FMODE_* flags are clamped at u32.

6 bits remain at top and 4 bits just above O_ACCMODE, so there is no immediate
danger of overflow and if any additional mode bits are needed they are
available.
000377777703 used
037777777777 available
10 bits remaining

So, I don't think a check at this point in the code is useful, but do agree
that there should be some changes and checks added in sys_openat2 and
build_open_flags().


Also noticed: It looks like fddb5d430ad9f left in VALID_UPGRADE_FLAGS for
how->upgrade_mask that was removed.  This may be used at a later date, but at
this point is dead code.

quoted

Christian

- RGB

- RGB

--
Richard Guy Briggs [off-list ref]
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

On Thu, Apr 22, 2021 at 10:34:08PM -0400, Richard Guy Briggs wrote:

On 2021-03-18 08:08, Richard Guy Briggs wrote:

quoted

On 2021-03-18 11:48, Christian Brauner wrote:

quoted

[+Cc Aleksa, the author of openat2()]

Ah!  Thanks for pulling in Aleksa.  I thought I caught everyone...

quoted

and a comment below. :)

Same...

quoted

On Wed, Mar 17, 2021 at 09:47:17PM -0400, Richard Guy Briggs wrote:

quoted

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 <redacted>
---
 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?

Ah, ok, fair enough, since original flags use a u32 and this was picked
as u64 for alignment.  It was just occurring to me last night that I
might have the dubious honour of being the first usage of 0%llo format
specifier in the kernel...  ;-)

quoted

quoted

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.)

open_how arguments are translated to open_flags which is limited to 32 bits.

This code is shared with the other open functions that are limited to 32 bits
in open_flags.  openat2 was created to avoid the limitations of openat, so at
some point it isn't unreasonable that flags exceed 32 bits, but open_flags
would have to be modified at that point to accommodate.

This value is handed in from userspace, and could be handed in without being
defined in the kernel, so those values need to be properly checked regardless
of the flags defined in the kernel.

The openat2 syscall claims to check all flags but no check is done on the top
32 bits.

Hm, I think this is an oversight because of the different semantics for
openat() and openat2(). We should check that no upper 32 bits are set
for openat2(). That's the intended semantics. For old openat()
we can't error on unknown flags because it has traditionally ignored
unknown flags.

build_open_flags() assigns how->flags to an int, effectively dropping the top
32 bits, before being checked against ~VALID_OPEN_FLAGS.  This happens after
audit mode filtering, but has the same result.

Right. That's at bug we should return an error to userspace. We do for
any unkown values that fall within the lower 32 bit range so it's silly
to ignore unknown values in the upper 32 bit range.

Audit mode filtering using ACC_MODE() already masks out all but the lowest two
bits with O_ACCMODE, so there is no danger of overflowing a u32.

tomoyo_check_open_permission() assigns ACC_MODE() to u8 without a check.

All FMODE_* flags are clamped at u32.

6 bits remain at top and 4 bits just above O_ACCMODE, so there is no immediate
danger of overflow and if any additional mode bits are needed they are
available.
000377777703 used
037777777777 available
10 bits remaining

So, I don't think a check at this point in the code is useful, but do agree

Maybe but note that a defensive posture here might be a good thing
instead of tripping over the issue later.

that there should be some changes and checks added in sys_openat2 and
build_open_flags().


Also noticed: It looks like fddb5d430ad9f left in VALID_UPGRADE_FLAGS for
how->upgrade_mask that was removed.  This may be used at a later date, but at
this point is dead code.

I'll take a look now.

Christian