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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@ubuntu.com>
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@ -2,6 +2,9 @@
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* login/openpty.c (openpty): Close slave pty file descriptor on error.
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* login/openpty.c (openpty): If defined, use the TIOCGPTPEER ioctl()
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call to allocate the slave pty file descriptor.
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2017-10-06 Joseph Myers <joseph@codesourcery.com>
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* sysdeps/ieee754/ldbl-128/s_fma.c: Include <libm-alias-double.h>.
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@ -94,6 +94,8 @@ openpty (int *amaster, int *aslave, char *name,
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char *buf = _buf;
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int master, ret = -1, slave = -1;
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*buf = '\0';
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master = getpt ();
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if (master == -1)
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return -1;
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@ -104,12 +106,22 @@ openpty (int *amaster, int *aslave, char *name,
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if (unlockpt (master))
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goto on_error;
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if (pts_name (master, &buf, sizeof (_buf)))
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goto on_error;
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slave = open (buf, O_RDWR | O_NOCTTY);
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#ifdef TIOCGPTPEER
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/* Try to allocate slave fd solely based on master fd first. */
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slave = ioctl (master, TIOCGPTPEER, O_RDWR | O_NOCTTY);
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#endif
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if (slave == -1)
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goto on_error;
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{
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/* Fallback to path-based slave fd allocation in case kernel doesn't
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* support TIOCGPTPEER.
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*/
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if (pts_name (master, &buf, sizeof (_buf)))
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goto on_error;
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slave = open (buf, O_RDWR | O_NOCTTY);
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if (slave == -1)
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goto on_error;
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}
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/* XXX Should we ignore errors here? */
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if (termp)
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@ -122,7 +134,13 @@ openpty (int *amaster, int *aslave, char *name,
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*amaster = master;
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*aslave = slave;
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if (name != NULL)
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strcpy (name, buf);
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{
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if (*buf == '\0')
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if (pts_name (master, &buf, sizeof (_buf)))
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goto on_error;
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strcpy (name, buf);
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}
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ret = 0;
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