@@ -2138,8 +2138,24 @@ retry_open:
if (!noctty &&
current->signal->leader &&
!current->signal->tty &&
- tty->session == NULL)
- __proc_set_tty(tty);
+ tty->session == NULL) {
+ /*
+ * Don't let a process that only has write access to the tty
+ * obtain the privileges associated with having a tty as
+ * controlling terminal (being able to reopen it with full
+ * access through /dev/tty, being able to perform pushback).
+ * Many distributions set the group of all ttys to "tty" and
+ * grant write-only access to all terminals for setgid tty
+ * binaries, which should not imply full privileges on all ttys.
+ *
+ * This could theoretically break old code that performs open()
+ * on a write-only file descriptor. In that case, it might be
+ * necessary to also permit this if
+ * inode_permission(inode, MAY_READ) == 0.
+ */
+ if (filp->f_mode & FMODE_READ)
+ __proc_set_tty(tty);
+ }
spin_unlock_irq(¤t->sighand->siglock);
read_unlock(&tasklist_lock);
tty_unlock(tty);
@@ -2428,7 +2444,7 @@ static int fionbio(struct file *file, int __user *p)
* Takes ->siglock() when updating signal->tty
*/
-static int tiocsctty(struct tty_struct *tty, int arg)
+static int tiocsctty(struct tty_struct *tty, struct file *file, int arg)
{
int ret = 0;
@@ -2462,6 +2478,13 @@ static int tiocsctty(struct tty_struct *tty, int arg)
goto unlock;
}
}
+
+ /* See the comment in tty_open(). */
+ if ((file->f_mode & FMODE_READ) == 0 && !capable(CAP_SYS_ADMIN)) {
+ ret = -EPERM;
+ goto unlock;
+ }
+
proc_set_tty(tty);
unlock:
read_unlock(&tasklist_lock);
@@ -2854,7 +2877,7 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
no_tty();
return 0;
case TIOCSCTTY:
- return tiocsctty(tty, arg);
+ return tiocsctty(tty, file, arg);
case TIOCGPGRP:
return tiocgpgrp(tty, real_tty, p);
case TIOCSPGRP:
This is a note to let you know that I have just added a patch titled drivers/tty: require read access for controlling terminal to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue This patch is scheduled to be released in version 3.19.8-ckt10. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.19.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 4741210ec72d04482ff5739d0d0d3659a7d86824 Mon Sep 17 00:00:00 2001 From: Jann Horn <jann@thejh.net> Date: Sun, 4 Oct 2015 19:29:12 +0200 Subject: [PATCH 023/120] drivers/tty: require read access for controlling terminal commit 0c55627167870255158db1cde0d28366f91c8872 upstream. This is mostly a hardening fix, given that write-only access to other users' ttys is usually only given through setgid tty executables. Signed-off-by: Jann Horn <jann@thejh.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/tty/tty_io.c | 31 +++++++++++++++++++++++++++---- 1 file changed, 27 insertions(+), 4 deletions(-) -- 1.9.1