2017-10-31 13:24:35 -04:00
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From dd42bf1197144ede075a9d4793123f7689e164bc Mon Sep 17 00:00:00 2001
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From: Peter Hurley <peter@hurleysoftware.com>
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Date: Fri, 27 Nov 2015 14:30:21 -0500
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Subject: tty: Prevent ldisc drivers from re-using stale tty fields
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Line discipline drivers may mistakenly misuse ldisc-related fields
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when initializing. For example, a failure to initialize tty->receive_room
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in the N_GIGASET_M101 line discipline was recently found and fixed [1].
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Now, the N_X25 line discipline has been discovered accessing the previous
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line discipline's already-freed private data [2].
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Harden the ldisc interface against misuse by initializing revelant
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tty fields before instancing the new line discipline.
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[1]
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commit fd98e9419d8d622a4de91f76b306af6aa627aa9c
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Author: Tilman Schmidt <tilman@imap.cc>
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Date: Tue Jul 14 00:37:13 2015 +0200
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isdn/gigaset: reset tty->receive_room when attaching ser_gigaset
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[2] Report from Sasha Levin <sasha.levin@oracle.com>
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[ 634.336761] ==================================================================
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[ 634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0
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[ 634.339558] Read of size 4 by task syzkaller_execu/8981
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[ 634.340359] =============================================================================
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[ 634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected
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...
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[ 634.405018] Call Trace:
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[ 634.405277] dump_stack (lib/dump_stack.c:52)
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[ 634.405775] print_trailer (mm/slub.c:655)
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[ 634.406361] object_err (mm/slub.c:662)
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[ 634.406824] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236)
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[ 634.409581] __asan_report_load4_noabort (mm/kasan/report.c:279)
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[ 634.411355] x25_asy_open_tty (drivers/net/wan/x25_asy.c:559 (discriminator 1))
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[ 634.413997] tty_ldisc_open.isra.2 (drivers/tty/tty_ldisc.c:447)
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[ 634.414549] tty_set_ldisc (drivers/tty/tty_ldisc.c:567)
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[ 634.415057] tty_ioctl (drivers/tty/tty_io.c:2646 drivers/tty/tty_io.c:2879)
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[ 634.423524] do_vfs_ioctl (fs/ioctl.c:43 fs/ioctl.c:607)
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[ 634.427491] SyS_ioctl (fs/ioctl.c:622 fs/ioctl.c:613)
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[ 634.427945] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188)
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Cc: Tilman Schmidt <tilman@imap.cc>
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Cc: Sasha Levin <sasha.levin@oracle.com>
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Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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drivers/tty/tty_ldisc.c | 7 +++++++
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1 file changed, 7 insertions(+)
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diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
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index 9ec1250..a054d03 100644
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--- a/drivers/tty/tty_ldisc.c
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+++ b/drivers/tty/tty_ldisc.c
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@@ -417,6 +417,10 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush);
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* they are not on hot paths so a little discipline won't do
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* any harm.
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*
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+ * The line discipline-related tty_struct fields are reset to
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+ * prevent the ldisc driver from re-using stale information for
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+ * the new ldisc instance.
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+ *
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* Locking: takes termios_rwsem
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*/
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@@ -425,6 +429,9 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
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down_write(&tty->termios_rwsem);
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tty->termios.c_line = num;
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up_write(&tty->termios_rwsem);
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+
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+ tty->disc_data = NULL;
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+ tty->receive_room = 0;
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}
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/**
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--
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cgit v1.1
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