diff options
| author | Jann Horn <jann@thejh.net> | 2015-10-04 19:29:12 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-10-22 14:43:26 -0700 |
| commit | 9f98531e220596953ce62c5df084bf073d88f901 (patch) | |
| tree | a54c429acbe2742e42b2ed61a859348c8b044a6c | |
| parent | 614ea4ea2c3face1f54dcc8e9a0ba134adce427e (diff) | |
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>
| -rw-r--r-- | drivers/tty/tty_io.c | 31 |
1 files changed, 27 insertions, 4 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e5695467598f..21837f14a403 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2144,8 +2144,24 @@ 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); @@ -2434,7 +2450,7 @@ 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; @@ -2468,6 +2484,13 @@ 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); @@ -2860,7 +2883,7 @@ 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: |