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Date: Fri, 1 Sep 2017 17:35:58 +0200
From: Christian Brauner <christian.brauner@...ntu.com>
To: musl@...ts.openwall.com
Cc: Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH 1/1] openpty: use TIOCGPTPEER to open slave side fd
Newer kernels expose the ioctl TIOCGPTPEER [1] call to userspace which allows to
safely allocate a file descriptor for a pty slave based solely on the master
file descriptor. This allows us to avoid path-based operations and makes this
function a lot safer in the face of devpts mounts in different mount namespaces.
[1]: https://patchwork.kernel.org/patch/9760743/
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
src/misc/openpty.c | 34 +++++++++++++++++++++++++++++++---
1 file changed, 31 insertions(+), 3 deletions(-)
diff --git a/src/misc/openpty.c b/src/misc/openpty.c
index c1074060..9eab7a37 100644
--- a/src/misc/openpty.c
+++ b/src/misc/openpty.c
@@ -3,13 +3,14 @@
#include <unistd.h>
#include <pty.h>
#include <stdio.h>
+#include <string.h>
#include <pthread.h>
/* Nonstandard, but vastly superior to the standard functions */
int openpty(int *pm, int *ps, char *name, const struct termios *tio, const struct winsize *ws)
{
- int m, s, n=0, cs;
+ int m, s = -1, cs;
char buf[20];
m = open("/dev/ptmx", O_RDWR|O_NOCTTY);
@@ -17,13 +18,38 @@ int openpty(int *pm, int *ps, char *name, const struct termios *tio, const struc
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+ if (!name) name = buf;
+
+#ifdef TIOCGPTPEER
+ int ret;
+
+ /* Try to allocate slave fd solely based on the master fd in case the
+ * kernel supports it.
+ */
+ s = ioctl(m, TIOCGPTPEER, O_RDWR|O_NOCTTY);
+ if (s < 0)
+ goto fail;
+
+ /* Check the contents of the symlink in case devpts has been mounted in
+ * a non-standard location.
+ */
+ ret = ttyname_r(s, name, sizeof buf);
+ if (ret)
+ goto fail;
+
+ if (strncmp(name, "/dev/pts/", 9))
+ goto fail;
+#else
+ int n = 0;
+
if (ioctl(m, TIOCSPTLCK, &n) || ioctl (m, TIOCGPTN, &n))
goto fail;
- if (!name) name = buf;
snprintf(name, sizeof buf, "/dev/pts/%d", n);
- if ((s = open(name, O_RDWR|O_NOCTTY)) < 0)
+ s = open(name, O_RDWR|O_NOCTTY);
+ if (s < 0)
goto fail;
+#endif
if (tio) tcsetattr(s, TCSANOW, tio);
if (ws) ioctl(s, TIOCSWINSZ, ws);
@@ -35,6 +61,8 @@ int openpty(int *pm, int *ps, char *name, const struct termios *tio, const struc
return 0;
fail:
close(m);
+ if (s >= 0)
+ close(s);
pthread_setcancelstate(cs, 0);
return -1;
}
--
2.14.1
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