[PATCH] audit: handle unknown status requests in audit_receive_msg

[Ricardo Robaina]

Currently, audit_receive_msg() ignores unknown status bits in AUDIT_SET
requests, incorrectly returning success to newer user space tools
querying unsupported features. This breaks forward compatibility.

Fix this by defining AUDIT_STATUS_ALL in the UAPI header and returning
-EINVAL if any unrecognized bits are set (s.mask & ~AUDIT_STATUS_ALL).
This ensures invalid requests are safely rejected, allowing user space
to reliably test for and gracefully handle feature detection on older
kernels.

Suggested-by: Steve Grubb <sgrubb@xxxxxxxxxx>
Signed-off-by: Ricardo Robaina <rrobaina@xxxxxxxxxx>
---
 include/uapi/linux/audit.h | 9 +++++++++
 kernel/audit.c             | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 14a1c1fe013a..1d5122b9274a 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -356,6 +356,15 @@ enum {
 #define AUDIT_STATUS_LOST			0x0040
 #define AUDIT_STATUS_BACKLOG_WAIT_TIME_ACTUAL	0x0080
 
+#define AUDIT_STATUS_ALL (AUDIT_STATUS_ENABLED | \
+			  AUDIT_STATUS_FAILURE | \
+			  AUDIT_STATUS_PID | \
+			  AUDIT_STATUS_RATE_LIMIT | \
+			  AUDIT_STATUS_BACKLOG_LIMIT | \
+			  AUDIT_STATUS_BACKLOG_WAIT_TIME | \
+			  AUDIT_STATUS_LOST | \
+			  AUDIT_STATUS_BACKLOG_WAIT_TIME_ACTUAL)
+
 #define AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT	0x00000001
 #define AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME	0x00000002
 #define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH	0x00000004
diff --git a/kernel/audit.c b/kernel/audit.c
index 5a0216056524..592383dce090 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1295,6 +1295,8 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 		memset(&s, 0, sizeof(s));
 		/* guard against past and future API changes */
 		memcpy(&s, data, min_t(size_t, sizeof(s), data_len));
+		if (s.mask & ~AUDIT_STATUS_ALL)
+			return -EINVAL;
 		if (s.mask & AUDIT_STATUS_ENABLED) {
 			err = audit_set_enabled(s.enabled);
 			if (err < 0)
-- 
2.53.0