| Message ID | 20170826134449.26527-2-christian.brauner@ubuntu.com |
|---|---|
| State | New |
| Headers | show |
On 08/26/2017 03:44 PM, Christian Brauner wrote: > +#ifdef TIOCGPTPEER > + slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY); > +#else > if (pts_name (master, &buf, sizeof (_buf))) > goto fail; > > slave = open (buf, O_RDWR | O_NOCTTY); > +#endif I don't think you can #ifdef out existing code this way without introducing failures on older kernels. You need to try the ioctl first, and if that fails, use the old pts_name code. Thanks, Florian
On Mon, Aug 28, 2017 at 09:34:11AM +0200, Florian Weimer wrote: > On 08/26/2017 03:44 PM, Christian Brauner wrote: > > +#ifdef TIOCGPTPEER > > + slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY); > > +#else > > if (pts_name (master, &buf, sizeof (_buf))) > > goto fail; > > > > slave = open (buf, O_RDWR | O_NOCTTY); > > +#endif > > I don't think you can #ifdef out existing code this way without > introducing failures on older kernels. You need to try the ioctl first, > and if that fails, use the old pts_name code. Cool. Will resend the [PATCH 2/2] soon. I take it that [PATH 1/1] holds up as it stands. Thanks! Christian > > Thanks, > Florian
On Mon, 28 Aug 2017, Florian Weimer wrote: > On 08/26/2017 03:44 PM, Christian Brauner wrote: > > +#ifdef TIOCGPTPEER > > + slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY); > > +#else > > if (pts_name (master, &buf, sizeof (_buf))) > > goto fail; > > > > slave = open (buf, O_RDWR | O_NOCTTY); > > +#endif > > I don't think you can #ifdef out existing code this way without > introducing failures on older kernels. You need to try the ioctl first, > and if that fails, use the old pts_name code. And in principle there should be appropriate __ASSUME_* conditionals so that when building with a new-enough --enable-kernel the old code can be conditioned out (however, because this code is not Linux-specific, the old case would need to stay in the code even when __ASSUME_TIOCGPTPEER is defined unconditionally in the Linux kernel-features.h).
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 8fbc66a3ef..293cc0a0db 100644 --- a/login/openpty.c +++ b/login/openpty.c @@ -104,10 +104,14 @@ openpty (int *amaster, int *aslave, char *name, if (unlockpt (master)) goto fail; +#ifdef TIOCGPTPEER + slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY); +#else if (pts_name (master, &buf, sizeof (_buf))) goto fail; slave = open (buf, O_RDWR | O_NOCTTY); +#endif if (slave == -1) { if (buf != _buf) @@ -127,7 +131,13 @@ openpty (int *amaster, int *aslave, char *name, *amaster = master; *aslave = slave; if (name != NULL) - strcpy (name, buf); + { +#ifdef TIOCGPTPEER + if (pts_name (master, &buf, sizeof (_buf))) + goto fail; +#endif + strcpy (name, buf); + } if (buf != _buf) free (buf);
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 | 5 +++++ login/openpty.c | 12 +++++++++++- 2 files changed, 16 insertions(+), 1 deletion(-)