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

1 files changed, 10 insertions, 1 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_ */