libc/stdio: Fail fdopen() on an execute-only fd.

An execute-only fd (opened with O_EXEC) allows neither read() nor write()
and is therefore incompatible with all stdio modes. Therefore, the [EINVAL]
error applies.

Also adjust the similar check in freopen() with a NULL path, even though
this checks an fd which is already from a FILE.

2 files changed, 5 insertions, 3 deletions

diff --git a/lib/libc/stdio/fdopen.c b/lib/libc/stdio/fdopen.c
index 2e19b9f..b936998 100644
--- a/lib/libc/stdio/fdopen.c
+++ b/lib/libc/stdio/fdopen.c
@@ -70,7 +70,8 @@ fdopen(int fd, const char *mode)
 	/* Make sure the mode the user wants is a subset of the actual mode. */
 	if ((fdflags = _fcntl(fd, F_GETFL, 0)) < 0)
 		return (NULL);
-	tmp = fdflags & O_ACCMODE;
+	/* Work around incorrect O_ACCMODE. */
+	tmp = fdflags & (O_ACCMODE | O_EXEC);
 	if (tmp != O_RDWR && (tmp != (oflags & O_ACCMODE))) {
 		errno = EINVAL;
 		return (NULL);
diff --git a/lib/libc/stdio/freopen.c b/lib/libc/stdio/freopen.c
index dc5508d..0ff83bf 100644
--- a/lib/libc/stdio/freopen.c
+++ b/lib/libc/stdio/freopen.c
@@ -92,8 +92,9 @@ freopen(const char * __restrict file, const char * __restrict mode,
 			errno = sverrno;
 			return (NULL);
 		}
-		if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
-		    (oflags & O_ACCMODE)) {
+		/* Work around incorrect O_ACCMODE. */
+		if ((dflags & O_ACCMODE) != O_RDWR &&
+		    (dflags & (O_ACCMODE | O_EXEC)) != (oflags & O_ACCMODE)) {
 			fclose(fp);
 			FUNLOCKFILE(fp);
 			errno = EINVAL;