[PATCH 1/2] seccomp: Allow for auditing functionality specific to return actions

[Tyler Hicks <tyhicks@canonical.com>]

This patch introduces the concept of auditing formats that are specific
to the action specified in a filter's return value. Initially, only
SECCOMP_RET_KILL has an auditing message that differs from other return
actions because it specifies the signal that is to be sent.

This patch causes a small functional change in that "sig=0" is not
printed when auditing seccomp actions other than SECCOMP_RET_KILL.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 include/linux/audit.h | 39 +++++++++++++++++++++++++++++++++------
 kernel/auditsc.c      | 19 +++++++++++++++----
 kernel/seccomp.c      |  6 +++---
 3 files changed, 51 insertions(+), 13 deletions(-)

diff --git a/include/linux/audit.h b/include/linux/audit.h
index f51fca8d..8c588c3 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -85,6 +85,11 @@ struct audit_field {
 	u32				op;
 };
 
+struct audit_seccomp_info {
+	int		code;
+	long		signr;
+};
+
 extern int is_audit_feature_set(int which);
 
 extern int __init audit_register_class(int class, unsigned *list);
@@ -243,7 +248,8 @@ extern void __audit_file(const struct file *);
 extern void __audit_inode_child(struct inode *parent,
 				const struct dentry *dentry,
 				const unsigned char type);
-extern void __audit_seccomp(unsigned long syscall, long signr, int code);
+extern void __audit_seccomp(unsigned long syscall,
+			    struct audit_seccomp_info *info);
 extern void __audit_ptrace(struct task_struct *t);
 
 static inline bool audit_dummy_context(void)
@@ -313,14 +319,31 @@ static inline void audit_inode_child(struct inode *parent,
 }
 void audit_core_dumps(long signr);
 
-static inline void audit_seccomp(unsigned long syscall, long signr, int code)
+static inline void audit_seccomp_signal(unsigned long syscall, long signr,
+					int code)
 {
 	if (!audit_enabled)
 		return;
 
 	/* Force a record to be reported if a signal was delivered. */
-	if (signr || unlikely(!audit_dummy_context()))
-		__audit_seccomp(syscall, signr, code);
+	if (signr || unlikely(!audit_dummy_context())) {
+		struct audit_seccomp_info info = { .code = code,
+						   .signr = signr };
+
+		__audit_seccomp(syscall, &info);
+	}
+}
+
+static inline void audit_seccomp_common(unsigned long syscall, int code)
+{
+	if (!audit_enabled)
+		return;
+
+	if (code || unlikely(!audit_dummy_context())) {
+		struct audit_seccomp_info info = { .code = code };
+
+		__audit_seccomp(syscall, &info);
+	}
 }
 
 static inline void audit_ptrace(struct task_struct *t)
@@ -485,9 +508,13 @@ static inline void audit_inode_child(struct inode *parent,
 { }
 static inline void audit_core_dumps(long signr)
 { }
-static inline void __audit_seccomp(unsigned long syscall, long signr, int code)
+static inline void __audit_seccomp(unsigned long syscall,
+				   struct audit_seccomp_info *info);
+{ }
+static inline void audit_seccomp_signal(unsigned long syscall, long signr,
+					int code)
 { }
-static inline void audit_seccomp(unsigned long syscall, long signr, int code)
+static inline void audit_seccomp_common(unsigned long syscall, int code)
 { }
 static inline int auditsc_get_stamp(struct audit_context *ctx,
 			      struct timespec *t, unsigned int *serial)
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index cf1fa43..b3472f2 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -74,6 +74,7 @@
 #include <linux/string.h>
 #include <linux/uaccess.h>
 #include <uapi/linux/limits.h>
+#include <uapi/linux/seccomp.h>
 
 #include "audit.h"
 
@@ -2415,7 +2416,7 @@ void audit_core_dumps(long signr)
 	audit_log_end(ab);
 }
 
-void __audit_seccomp(unsigned long syscall, long signr, int code)
+void __audit_seccomp(unsigned long syscall, struct audit_seccomp_info *info)
 {
 	struct audit_buffer *ab;
 
@@ -2423,9 +2424,19 @@ void __audit_seccomp(unsigned long syscall, long signr, int code)
 	if (unlikely(!ab))
 		return;
 	audit_log_task(ab);
-	audit_log_format(ab, " sig=%ld arch=%x syscall=%ld compat=%d ip=0x%lx code=0x%x",
-			 signr, syscall_get_arch(), syscall,
-			 in_compat_syscall(), KSTK_EIP(current), code);
+
+	switch (info->code) {
+	case SECCOMP_RET_KILL:
+		audit_log_format(ab, " sig=%ld", info->signr);
+		break;
+	default:
+		break;
+	}
+
+	audit_log_format(ab,
+			 " arch=%x syscall=%ld compat=%d ip=0x%lx code=0x%x",
+			 syscall_get_arch(), syscall, in_compat_syscall(),
+			 KSTK_EIP(current), info->code);
 	audit_log_end(ab);
 }
 
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index f7ce79a..54c01b6 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -532,7 +532,7 @@ static void __secure_computing_strict(int this_syscall)
 #ifdef SECCOMP_DEBUG
 	dump_stack();
 #endif
-	audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
+	audit_seccomp_signal(this_syscall, SIGKILL, SECCOMP_RET_KILL);
 	do_exit(SIGKILL);
 }
 
@@ -635,14 +635,14 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 
 	case SECCOMP_RET_KILL:
 	default:
-		audit_seccomp(this_syscall, SIGSYS, action);
+		audit_seccomp_signal(this_syscall, SIGSYS, action);
 		do_exit(SIGSYS);
 	}
 
 	unreachable();
 
 skip:
-	audit_seccomp(this_syscall, 0, action);
+	audit_seccomp_common(this_syscall, action);
 	return -1;
 }
 #else
-- 
2.7.4