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c8bcd9c5be
Currently, locking of ->session is very inconsistent; most places protect it using the legacy tty mutex, but disassociate_ctty(), __do_SAK(), tiocspgrp() and tiocgsid() don't. Two of the writers hold the ctrl_lock (because they already need it for ->pgrp), but __proc_set_tty() doesn't do that yet. On a PREEMPT=y system, an unprivileged user can theoretically abuse this broken locking to read 4 bytes of freed memory via TIOCGSID if tiocgsid() is preempted long enough at the right point. (Other things might also go wrong, especially if root-only ioctls are involved; I'm not sure about that.) Change the locking on ->session such that: - tty_lock() is held by all writers: By making disassociate_ctty() hold it. This should be fine because the same lock can already be taken through the call to tty_vhangup_session(). The tricky part is that we need to shorten the area covered by siglock to be able to take tty_lock() without ugly retry logic; as far as I can tell, this should be fine, since nothing in the signal_struct is touched in the `if (tty)` branch. - ctrl_lock is held by all writers: By changing __proc_set_tty() to hold the lock a little longer. - All readers that aren't holding tty_lock() hold ctrl_lock: By adding locking to tiocgsid() and __do_SAK(), and expanding the area covered by ctrl_lock in tiocspgrp(). Cc: stable@kernel.org Signed-off-by: Jann Horn <jannh@google.com> Reviewed-by: Jiri Slaby <jirislaby@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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hvc | ||
ipwireless | ||
serdev | ||
serial | ||
vt | ||
amiserial.c | ||
cyclades.c | ||
ehv_bytechan.c | ||
goldfish.c | ||
isicom.c | ||
Kconfig | ||
Makefile | ||
mips_ejtag_fdc.c | ||
moxa.c | ||
moxa.h | ||
mxser.c | ||
mxser.h | ||
n_gsm.c | ||
n_hdlc.c | ||
n_null.c | ||
n_r3964.c | ||
n_tracerouter.c | ||
n_tracesink.c | ||
n_tracesink.h | ||
n_tty.c | ||
nozomi.c | ||
pty.c | ||
rocket_int.h | ||
rocket.c | ||
rocket.h | ||
synclink_gt.c | ||
synclink.c | ||
synclinkmp.c | ||
sysrq.c | ||
tty_audit.c | ||
tty_baudrate.c | ||
tty_buffer.c | ||
tty_io.c | ||
tty_ioctl.c | ||
tty_jobctrl.c | ||
tty_ldisc.c | ||
tty_ldsem.c | ||
tty_mutex.c | ||
tty_port.c | ||
ttynull.c | ||
vcc.c |