From 1a0220ebac77da3d9e2989528e64e1683c63fb58 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 27 Nov 2015 14:30:21 -0500 Subject: [PATCH] BACKPORT: tty: Prevent ldisc drivers from re-using stale tty fields (cherry picked from commit dd42bf1197144ede075a9d4793123f7689e164bc) Line discipline drivers may mistakenly misuse ldisc-related fields when initializing. For example, a failure to initialize tty->receive_room in the N_GIGASET_M101 line discipline was recently found and fixed [1]. Now, the N_X25 line discipline has been discovered accessing the previous line discipline's already-freed private data [2]. Harden the ldisc interface against misuse by initializing revelant tty fields before instancing the new line discipline. [1] commit fd98e9419d8d622a4de91f76b306af6aa627aa9c Author: Tilman Schmidt Date: Tue Jul 14 00:37:13 2015 +0200 isdn/gigaset: reset tty->receive_room when attaching ser_gigaset [2] Report from Sasha Levin [ 634.336761] ================================================================== [ 634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0 [ 634.339558] Read of size 4 by task syzkaller_execu/8981 [ 634.340359] ============================================================================= [ 634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected ... [ 634.405018] Call Trace: [ 634.405277] dump_stack (lib/dump_stack.c:52) [ 634.405775] print_trailer (mm/slub.c:655) [ 634.406361] object_err (mm/slub.c:662) [ 634.406824] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236) [ 634.409581] __asan_report_load4_noabort (mm/kasan/report.c:279) [ 634.411355] x25_asy_open_tty (drivers/net/wan/x25_asy.c:559 (discriminator 1)) [ 634.413997] tty_ldisc_open.isra.2 (drivers/tty/tty_ldisc.c:447) [ 634.414549] tty_set_ldisc (drivers/tty/tty_ldisc.c:567) [ 634.415057] tty_ioctl (drivers/tty/tty_io.c:2646 drivers/tty/tty_io.c:2879) [ 634.423524] do_vfs_ioctl (fs/ioctl.c:43 fs/ioctl.c:607) [ 634.427491] SyS_ioctl (fs/ioctl.c:622 fs/ioctl.c:613) [ 634.427945] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188) Cc: Tilman Schmidt Cc: Sasha Levin Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman Change-Id: Ibed6feadfb9706d478f93feec3b240aecfc64af3 Bug: 30951112 --- drivers/tty/tty_ldisc.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index b7b8048f12539..420dd6e52a279 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -415,6 +415,10 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush); * they are not on hot paths so a little discipline won't do * any harm. * + * The line discipline-related tty_struct fields are reset to + * prevent the ldisc driver from re-using stale information for + * the new ldisc instance. + * * Locking: takes termios_mutex */ @@ -423,6 +427,9 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num) mutex_lock(&tty->termios_mutex); tty->termios.c_line = num; mutex_unlock(&tty->termios_mutex); + + tty->disc_data = NULL; + tty->receive_room = 0; } /**