• Eric W. Biederman's avatar
    pty: Repair TIOCGPTPEER · 311fc65c
    Eric W. Biederman authored
    The implementation of TIOCGPTPEER has two issues.
    
    When /dev/ptmx (as opposed to /dev/pts/ptmx) is opened the wrong
    vfsmount is passed to dentry_open.  Which results in the kernel displaying
    the wrong pathname for the peer.
    
    The second is simply by caching the vfsmount and dentry of the peer it leaves
    them open, in a way they were not previously Which because of the inreased
    reference counts can cause unnecessary behaviour differences resulting in
    regressions.
    
    To fix these move the ioctl into tty_io.c at a generic level allowing
    the ioctl to have access to the struct file on which the ioctl is
    being called.  This allows the path of the slave to be derived when
    opening the slave through TIOCGPTPEER instead of requiring the path to
    the slave be cached.  Thus removing the need for caching the path.
    
    A new function devpts_ptmx_path is factored out of devpts_acquire and
    used to implement a function devpts_mntget.   The new function devpts_mntget
    takes a filp to perform the lookup on and fsi so that it can confirm
    that the superblock that is found by devpts_ptmx_path is the proper superblock.
    
    v2: Lots of fixes to make the code actually work
    v3: Suggestions by Linus
        - Removed the unnecessary initialization of filp in ptm_open_peer
        - Simplified devpts_ptmx_path as gotos are no longer required
    
    [ This is the fix for the issue that was reverted in commit
      143c97cc, but this time without breaking 'pbuilder' due to
      increased reference counts   - Linus ]
    
    Fixes: 54ebbfb1 ("tty: add TIOCGPTPEER ioctl")
    Reported-by: 's avatarChristian Brauner <christian.brauner@canonical.com>
    Reported-and-tested-by: 's avatarStefan Lippers-Hollmann <s.l-h@gmx.de>
    Signed-off-by: 's avatar"Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    311fc65c
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