commit dd42bf1197144ede075a9d4793123f7689e164bc upstream.
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 <tilman@imap.cc>
Date: Tue Jul 14 00:37:13 2015 +0200
isdn/gigaset: reset tty->receive_room when attaching ser_gigaset
[2] Report from Sasha Levin <sasha.levin@oracle.com>
[ 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 <tilman@imap.cc>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[wt: adjust context]
Signed-off-by: Willy Tarreau <w@1wt.eu>
tty_ioctl() already waits until sent. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Now that tty_ldisc_assign() is a one-line file-scoped function, remove it and perform the simple assignment at its call sites. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Merge get_ldisc() into its only call site.
Note how, after merging, the unsafe acquire of an ldisc reference
is obvious.
CPU 0 in tty_ldisc_try() | CPU 1 in tty_ldisc_halt()
|
test_bit(TTY_LDISC, &tty_flags) |
if (true) | clear_bit(TTY_LDISC, &tty_flags)
tty->ldisc != 0? | atomic_read(&tty->ldisc->users)
if (true) | ret_val == 1?
atomic_inc(&tty->ldisc->users) | if (false)
| wait
|
<goes on assuming safe ldisc use> | <doesn't wait - proceeds w/ close>
|
The spin lock in tty_ldisc_try() does nothing wrt synchronizing
the ldisc halt since it's not acquired as part of halting.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tty_ldisc_ref()/tty_ldisc_unref() have usage semantics equivalent to down_read_trylock()/up_read(). Only callers of tty_ldisc_put() are performing the additional operations necessary for proper ldisc teardown, and then only after ensuring no outstanding 'read lock' remains. Thus, tty_ldisc_unref() should never be the last reference; WARN if it is. Conversely, tty_ldisc_put() should never be destructing if the use count != 1. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Expected typical debug log: [ 582.721965] tty_open: opening pts3... [ 582.721970] tty_open: opening pts3... [ 582.721977] tty_release: pts3 (tty count=3)... [ 582.721980] tty_release: ptm3 (tty count=1)... [ 582.722015] pts3 vhangup... [ 582.722020] tty_ldisc_hangup: pts3: closing ldisc: ffff88007a920540 [ 582.724128] tty_release: pts3 (tty count=2)... [ 582.724217] tty_ldisc_hangup: pts3: re-opened ldisc: ffff88007a920580 [ 582.724221] tty_release: ptm3: final close [ 582.724234] tty_ldisc_release: ptm3: closing ldisc: ffff88007a920a80 [ 582.724238] tty_ldisc_release: ptm3: ldisc closed [ 582.724241] tty_release: ptm3: freeing structure... [ 582.724741] tty_open: opening pts3... Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This comment is a victim of code migration from "tty: Fix the ldisc hangup race"; re-parent it. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The tty core relies on the ldisc layer for synchronizing destruction of the tty. Instead, the final tty release must wait for any pending tty work to complete prior to tty destruction. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Waiting for buffer work to complete is not required for safely performing changes to the line discipline, once the line discipline is halted. The buffer work routine, flush_to_ldisc(), will be unable to acquire an ldisc ref and all existing references were waited until released (so it can't already have one). Ensure running buffer work which may reference the soon-to-be-gone tty completes and any buffer work running after this point retrieves a NULL tty. Also, ensure all buffer work is cancelled on port destruction. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>