[PATCH 14/27] selftests/landlock: Make audit_message large enough for any exe filter

["Günther Noack" <gnoack3000@gmail.com>]

audit_filter_exe() copies the filtered executable path after the
audit_rule_data header in struct audit_message.  The message buffer was
sized as PATH_MAX + 200 bytes with received records in mind, but
struct audit_rule_data alone takes 1040 bytes.  That leaves only 3256
bytes for the path, while the kernel accepts up to PATH_MAX bytes, so a
long path overflows the message.

Size the buffer for an audit_rule_data followed by a PATH_MAX string.
This only makes the buffer larger, so received records still fit.

Also check that the request fits in the message and return -E2BIG
otherwise, in case exe_len does not match the filter's buffer.

Assisted-by: LLM
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
---
 tools/testing/selftests/landlock/audit.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/landlock/audit.h b/tools/testing/selftests/landlock/audit.h
index 1e533b4e26db..173dcd1088db 100644
--- a/tools/testing/selftests/landlock/audit.h
+++ b/tools/testing/selftests/landlock/audit.h
@@ -41,7 +41,11 @@ struct audit_message {
 		struct audit_features features;
 		struct audit_rule_data rule;
 		struct nlmsgerr err;
-		char data[PATH_MAX + 200];
+		/*
+		 * Large enough for an audit_rule_data followed by a PATH_MAX
+		 * string (see audit_filter_exe()), and for received records.
+		 */
+		char data[sizeof(struct audit_rule_data) + PATH_MAX];
 	};
 };
 
@@ -171,6 +175,9 @@ static int audit_filter_exe(const int audit_fd,
 	if (filter->record_type != AUDIT_EXE)
 		return -EINVAL;
 
+	if (msg.header.nlmsg_len > sizeof(msg))
+		return -E2BIG;
+
 	memcpy(msg.rule.buf, filter->exe, filter->exe_len);
 	return audit_request(audit_fd, &msg, NULL);
 }
-- 
2.56.0