From: Christian Brauner <christian.brauner@ubuntu.com>
To: libc-alpha@sourceware.org, stgraber@stgraber.org,
serge@hallyn.com, fweimer@redhat.com, joseph@codesourcery.com
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH 2/2 v4] openpty: use TIOCGPTPEER to open slave side fd
Date: Tue, 29 Aug 2017 13:46:00 -0000 [thread overview]
Message-ID: <20170829134515.9345-2-christian.brauner@ubuntu.com> (raw)
In-Reply-To: <20170829134515.9345-1-christian.brauner@ubuntu.com>
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@ubuntu.com>
---
Changelog 2017-08-28:
* Instead of #ifdefing the TIOCGPTPEER ioctl flag we now try the ioctl() first
and if it fails we fallback to path-based allocation of the slave fd. This
allows us retain backward compatibility with kernels that do not support this
ioctl call.
* A note on the following codepath
if (name != NULL)
{
if (*buf == '\0')
if (pts_name (master, &buf, sizeof (_buf)))
goto fail;
strcpy (name, buf);
}
"buf" is guaranteed to be allocated in this case. If the pts_name() call above
failed we would have never reached this code path. If it has been called
succesfully it will either have handed us a valid buffer or "buf" will still
point to the static char array "_buf" which is initialized to 0.
Changelog 2017-08-28:
* Preserve #ifdef for TIOCGPTPEER since it needs to work on non-Linux distros
too.
* Only intialize first byte of "_buf".
Changelog 2017-08-29:
* Adapt to unified error handling as suggested by Florian.
---
ChangeLog | 5 +++++
login/openpty.c | 30 ++++++++++++++++++++++++------
2 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index bc5fb8e27f..30829e4c16 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-08-26 Christian Brauner <christian.brauner@ubuntu.com>
+
+ * login/openpty.c (openpty): If defined, use the TIOCGPTPEER ioctl call
+ to allocate the slave pty file descriptor.
+
2017-08-26 Christian Brauner <christian.brauner@ubuntu.com>
* login/openpty.c (openpty): Close slave pty file descriptor on error.
diff --git a/login/openpty.c b/login/openpty.c
index a7b1ab5dde..766aa958ff 100644
--- a/login/openpty.c
+++ b/login/openpty.c
@@ -94,6 +94,8 @@ openpty (int *amaster, int *aslave, char *name,
char *buf = _buf;
int master, ret = -1, slave = -1;
+ *buf = '\0';
+
master = getpt ();
if (master == -1)
return -1;
@@ -104,12 +106,22 @@ openpty (int *amaster, int *aslave, char *name,
if (unlockpt (master))
goto on_error;
- if (pts_name (master, &buf, sizeof (_buf)))
- goto on_error;
-
- slave = open (buf, O_RDWR | O_NOCTTY);
+#ifdef TIOCGPTPEER
+ /* Try to allocate slave fd solely based on master fd first. */
+ slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY);
+#endif
if (slave == -1)
- goto on_error;
+ {
+ /* Fallback to path-based slave fd allocation in case kernel doesn't
+ * support TIOCGPTPEER.
+ */
+ if (pts_name (master, &buf, sizeof (_buf)))
+ goto on_error;
+
+ slave = open (buf, O_RDWR | O_NOCTTY);
+ if (slave == -1)
+ goto on_error;
+ }
/* XXX Should we ignore errors here? */
if (termp)
@@ -122,7 +134,13 @@ openpty (int *amaster, int *aslave, char *name,
*amaster = master;
*aslave = slave;
if (name != NULL)
- strcpy (name, buf);
+ {
+ if (*buf == '\0')
+ if (pts_name (master, &buf, sizeof (_buf)))
+ goto on_error;
+
+ strcpy (name, buf);
+ }
ret = 0;
--
2.14.1
next prev parent reply other threads:[~2017-08-29 13:46 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-26 14:21 [PATCH 1/2] openpty: close slave pty fd on error Christian Brauner
2017-08-26 14:21 ` [PATCH 2/2] openpty: use TIOCGPTPEER to open slave side fd Christian Brauner
2017-08-28 7:34 ` Florian Weimer
2017-08-28 11:14 ` Christian Brauner
2017-08-28 11:39 ` Joseph Myers
2017-08-28 12:11 ` [PATCH 2/2 v2] " Christian Brauner
2017-08-28 12:22 ` Joseph Myers
2017-08-28 12:34 ` Andreas Schwab
2017-08-28 12:51 ` [PATCH 2/2 v3] " Christian Brauner
2017-08-29 9:07 ` [PATCH 1/2] openpty: close slave pty fd on error Florian Weimer
2017-08-29 13:46 ` [PATCH 1/2 v4] " Christian Brauner
2017-08-29 13:46 ` Christian Brauner [this message]
2017-08-29 14:00 ` Andreas Schwab
2017-08-29 14:12 ` Christian Brauner
2017-08-29 14:31 ` [PATCH 1/2 v5] " Christian Brauner
2017-08-29 14:31 ` [PATCH 2/2 v5] openpty: use TIOCGPTPEER to open slave side fd Christian Brauner
2017-09-10 17:45 ` [PATCH 1/2 v5] openpty: close slave pty fd on error Christian Brauner
2017-09-20 10:53 ` Christian Brauner
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