[PATCH v2] audit: do a quick exit when syscall number is invalid

[cgel.zte at gmail.com]

From: Yang Yang <yang.yang29 at zte.com.cn>

Userspace may use syscall with invalid syscall number by calling
syscall(syscall_num,..). For example we found openSSH may use
syscall with syscall number is -1 in some case. When that happens
we better do a quick handle no need to gohead.

Signed-off-by: Yang Yang <yang.yang29 at zte.com.cn>
Reported-by: Zeal Robot <zealci at zte.com.cn>
---
v2:
- fix compile error of arch/alpha, I have no alpha compile environment, so this fix
- is done by code review.
---
 arch/alpha/include/uapi/asm/unistd.h | 1 +
 kernel/auditsc.c                     | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/alpha/include/uapi/asm/unistd.h b/arch/alpha/include/uapi/asm/unistd.h
index 71fd5db06866..8115062216e4 100644
--- a/arch/alpha/include/uapi/asm/unistd.h
+++ b/arch/alpha/include/uapi/asm/unistd.h
@@ -13,5 +13,6 @@
 #define __NR_getgid	__NR_getxgid
 
 #include <asm/unistd_32.h>
+#include <asm-generic/unistd.h>
 
 #endif /* _UAPI_ALPHA_UNISTD_H */
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index ea2ee1181921..ea4915999e01 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2077,7 +2077,8 @@ void __audit_syscall_exit(int success, long return_code)
 	struct audit_context *context = audit_context();
 
 	if (!context || context->dummy ||
-	    context->context != AUDIT_CTX_SYSCALL)
+	    context->context != AUDIT_CTX_SYSCALL ||
+	    unlikely(context->major < 0 || context->major >= NR_syscalls))
 		goto out;
 
 	/* this may generate CONFIG_CHANGE records */
-- 
2.25.1