From 645ac9aaf89e3311949828546df6334322f48933 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Sun, 8 Oct 2017 14:10:46 +0200 Subject: 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 --- login/openpty.c | 30 ++++++++++++++++++++++++------ 1 file changed, 24 insertions(+), 6 deletions(-) (limited to 'login') diff --git a/login/openpty.c b/login/openpty.c index 9e556c27a5..6703128ea8 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; -- cgit 1.4.1