[PATCH 08/27] selftests/landlock: Handle a missing control message in recv_fd()

[Günther Noack]

CMSG_FIRSTHDR() returns NULL when recvmsg(2) did not receive any
ancillary data, e.g. when the peer closed the socket without sending an
FD.  recv_fd() dereferences the result unconditionally and crashes
instead of returning an error.

Return -EIO in that case.

Assisted-by: LLM
Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
---
 tools/testing/selftests/landlock/common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/landlock/common.h b/tools/testing/selftests/landlock/common.h
index c5124de68a51..e195c0f48eb3 100644
--- a/tools/testing/selftests/landlock/common.h
+++ b/tools/testing/selftests/landlock/common.h
@@ -158,7 +158,7 @@ static int __maybe_unused recv_fd(int usock)
 		return -errno;
 
 	cmsg = CMSG_FIRSTHDR(&msg);
-	if (cmsg->cmsg_len != CMSG_LEN(sizeof(fd_rx)))
+	if (!cmsg || cmsg->cmsg_len != CMSG_LEN(sizeof(fd_rx)))
 		return -EIO;
 
 	memcpy(&fd_rx, CMSG_DATA(cmsg), sizeof(fd_rx));
-- 
2.56.0