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da21d85025
This patch adds support for Unix98 pseudo terminals, that is, posix_openpt(3), grantpt(3), unlockpt(3), /dev/ptmx, and /dev/pts/. The latter is implemented with a new pseudo file system, PTYFS. In effect, this patch adds secure support for unprivileged pseudo terminal allocation, allowing programs such as tmux(1) to be used by non-root users as well. Test77 has been extended with new tests, and no longer needs to run as root. The new functionality is optional. To revert to the old behavior, remove the "ptyfs" entry from /etc/fstab. Technical nodes: o The reason for not implementing the NetBSD /dev/ptm approach is that implementing the corresponding ioctl (TIOCPTMGET) would require adding a number of extremely hairy exceptions to VFS, including the PTY driver having to create new file descriptors for its own device nodes. o PTYFS is required for Unix98 PTYs in order to avoid that the PTY driver has to be aware of old-style PTY naming schemes and even has to call chmod(2) on a disk-backed file system. PTY cannot be its own PTYFS since a character driver may currently not also be a file system. However, PTYFS may be subsumed into a DEVFS in the future. o The Unix98 PTY behavior differs somewhat from NetBSD's, in that slave nodes are created on ptyfs only upon the first call to grantpt(3). This approach obviates the need to revoke access as part of the grantpt(3) call. o Shutting down PTY may leave slave nodes on PTYFS, but once PTY is restarted, these leftover slave nodes will be removed before they create a security risk. Unmounting PTYFS will make existing PTY slaves permanently unavailable, and absence of PTYFS will block allocation of new Unix98 PTYs until PTYFS is (re)mounted. Change-Id: I822b43ba32707c8815fd0f7d5bb7a438f51421c1 |
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| LICENSE | ||
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