fix possible isatty false positives and unwanted device state changes

the equivalent checks for newly opened stdio output streams, used to
determine buffering mode, are also fixed.

on most archs, the TCGETS ioctl command shares a value with
SNDCTL_TMR_TIMEBASE, part of the OSS sound API which was apparently
used with certain MIDI and timer devices. for file descriptors
referring to such a device, TCGETS will not fail with ENOTTY as
expected; it may produce a different error, or may succeed, and if it
succeeds it changes the mode of the device. while it's unlikely that
such devices are in use, this is in principle very harmful behavior
for an operation which is supposed to do nothing but query whether the
fd refers to a tty.

TIOCGWINSZ, used to query logical window size for a terminal, was
chosen as an alternate ioctl to perform the isatty check. it does not
share a value with any other ioctl commands, and it succeeds on any
tty device.

this change also cleans up strace output to be less ugly and
misleading.

2 files changed, 4 insertions, 6 deletions

diff --git a/src/stdio/__fdopen.c b/src/stdio/__fdopen.c
index a6ae73a2..ef8f47dc 100644
--- a/src/stdio/__fdopen.c
+++ b/src/stdio/__fdopen.c
@@ -1,6 +1,5 @@
 #include "stdio_impl.h"
 #include <stdlib.h>
-#include <termios.h>
 #include <sys/ioctl.h>
 #include <fcntl.h>
 #include <errno.h>
@@ -9,7 +8,7 @@
 FILE *__fdopen(int fd, const char *mode)
 {
 	FILE *f;
-	struct termios tio;
+	struct winsize wsz;
 
 	/* Check for valid initial mode character */
 	if (!strchr("rwa", *mode)) {
@@ -43,7 +42,7 @@ FILE *__fdopen(int fd, const char *mode)
 
 	/* Activate line buffered mode for terminals */
 	f->lbf = EOF;
-	if (!(f->flags & F_NOWR) && !__syscall(SYS_ioctl, fd, TCGETS, &tio))
+	if (!(f->flags & F_NOWR) && !__syscall(SYS_ioctl, fd, TIOCGWINSZ, &wsz))
 		f->lbf = '\n';
 
 	/* Initialize op ptrs. No problem if some are unneeded. */
diff --git a/src/stdio/__stdout_write.c b/src/stdio/__stdout_write.c
index 200fe2c9..dd1ec60f 100644
--- a/src/stdio/__stdout_write.c
+++ b/src/stdio/__stdout_write.c
@@ -1,12 +1,11 @@
 #include "stdio_impl.h"
-#include <termios.h>
 #include <sys/ioctl.h>
 
 size_t __stdout_write(FILE *f, const unsigned char *buf, size_t len)
 {
-	struct termios tio;
+	struct winsize wsz;
 	f->write = __stdio_write;
-	if (!(f->flags & F_SVB) && __syscall(SYS_ioctl, f->fd, TCGETS, &tio))
+	if (!(f->flags & F_SVB) && __syscall(SYS_ioctl, f->fd, TIOCGWINSZ, &wsz))
 		f->lbf = -1;
 	return __stdio_write(f, buf, len);
 }