Ensure that libnv can be used when kern.trap_enotcap=1.

libnv used fcntl(fd, F_GETFL) to test whether fd is a valid file
descriptor.  Aside from being racy, this check requires CAP_FCNTL
rights on fd.  Instead, use fcntl(fd, F_GETFD), which does not require
any capability rights.

Also remove some redundant fd_is_valid() checks to avoid extra system
calls; in many cases we were performing this check immediately before
dup()ing the descriptor.

Reviewed by:	cem, oshogbo (previous version)
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D17963

3 files changed, 42 insertions, 12 deletions

diff --git a/lib/libnv/common_impl.h b/lib/libnv/common_impl.h
index a50902d221ce..69154466203a 100644
--- a/lib/libnv/common_impl.h
+++ b/lib/libnv/common_impl.h
@@ -34,6 +34,15 @@
 #ifndef	_COMMON_IMPL_H_
 #define	_COMMON_IMPL_H_
 
-#define	fd_is_valid(fd)	(fcntl((fd), F_GETFL) != -1 || errno != EBADF)
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+
+static inline bool
+fd_is_valid(int fd)
+{
+
+	return (fcntl(fd, F_GETFD) != -1 || errno != EBADF);
+}
 
 #endif	/* !_COMMON_IMPL_H_ */
diff --git a/lib/libnv/msgio.c b/lib/libnv/msgio.c
index 300a437a7421..938bca81b0ac 100644
--- a/lib/libnv/msgio.c
+++ b/lib/libnv/msgio.c
@@ -66,11 +66,6 @@ msghdr_add_fd(struct cmsghdr *cmsg, int fd)
 
 	PJDLOG_ASSERT(fd >= 0);
 
-	if (!fd_is_valid(fd)) {
-		errno = EBADF;
-		return (-1);
-	}
-
 	cmsg->cmsg_level = SOL_SOCKET;
 	cmsg->cmsg_type = SCM_RIGHTS;
 	cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
diff --git a/lib/libnv/tests/nvlist_send_recv_test.c b/lib/libnv/tests/nvlist_send_recv_test.c
index f4bc1c4464bc..1b673b5d4259 100644
--- a/lib/libnv/tests/nvlist_send_recv_test.c
+++ b/lib/libnv/tests/nvlist_send_recv_test.c
@@ -306,15 +306,12 @@ parent(int sock)
 	CHECK(name == NULL);
 }
 
-int
-main(void)
+static void
+send_nvlist(void)
 {
 	int status, socks[2];
 	pid_t pid;
 
-	printf("1..134\n");
-	fflush(stdout);
-
 	if (socketpair(PF_UNIX, SOCK_STREAM, 0, socks) < 0)
 		err(1, "socketpair() failed");
 	pid = fork();
@@ -326,7 +323,7 @@ main(void)
 		/* Child. */
 		close(socks[0]);
 		child(socks[1]);
-		return (0);
+		_exit(0);
 	default:
 		/* Parent. */
 		close(socks[1]);
@@ -336,6 +333,35 @@ main(void)
 
 	if (waitpid(pid, &status, 0) < 0)
 		err(1, "waitpid() failed");
+}
+
+static void
+send_closed_fd(void)
+{
+	nvlist_t *nvl;
+	int error, socks[2];
+
+	if (socketpair(PF_UNIX, SOCK_STREAM, 0, socks) < 0)
+		err(1, "socketpair() failed");
+
+	nvl = nvlist_create(0);
+	nvlist_add_descriptor(nvl, "fd", 12345);
+	error = nvlist_error(nvl);
+	CHECK(error == EBADF);
+
+	error = nvlist_send(socks[1], nvl);
+	CHECK(error != 0 && errno == EBADF);
+}
+
+int
+main(void)
+{
+
+	printf("1..136\n");
+	fflush(stdout);
+
+	send_nvlist();
+	send_closed_fd();
 
 	return (0);
 }