linux-stable.git/drivers/tty/tty_ldisc.c, branch linux-3.18.y

tty: ldisc: add sysctl to prevent autoloading of ldiscs

2019-04-27T07:30:25+00:00

commit 7c0cca7c847e6e019d67b7d793efbbe3b947d004 upstream.

By default, the kernel will automatically load the module of any line
dicipline that is asked for.  As this sometimes isn't the safest thing
to do, provide a sysctl to disable this feature.

By default, we set this to 'y' as that is the historical way that Linux
has worked, and we do not want to break working systems.  But in the
future, perhaps this can default to 'n' to prevent this functionality.

Signed-off-by: Greg Kroah-Hartman 
Reviewed-by: Theodore Ts'o 
Signed-off-by: Greg Kroah-Hartman

tty: Use __GFP_NOFAIL for tty_ldisc_get()

2018-05-02T14:59:54+00:00

commit bcdd0ca8cb8730573afebcaae4138f8f4c8eaa20 upstream.

syzbot is reporting crashes triggered by memory allocation fault injection
at tty_ldisc_get() [1]. As an attempt to handle OOM in a graceful way, we
have tried commit 5362544bebe85071 ("tty: don't panic on OOM in
tty_set_ldisc()"). But we reverted that attempt by commit a8983d01f9b7d600
("Revert "tty: don't panic on OOM in tty_set_ldisc()"") due to reproducible
crash. We should spend resource for finding and fixing race condition bugs
rather than complicate error paths for 2 * sizeof(void *) bytes allocation
failure.

[1] https://syzkaller.appspot.com/bug?id=489d33fa386453859ead58ff5171d43772b13aa3

Signed-off-by: Tetsuo Handa 
Reported-by: syzbot 
Cc: Michal Hocko 
Cc: Vegard Nossum 
Cc: Dmitry Vyukov 
Cc: Jiri Slaby 
Cc: Peter Hurley 
Cc: One Thousand Gnomes 
Cc: Linus Torvalds 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Greg Kroah-Hartman

tty: Prevent ldisc drivers from re-using stale tty fields

2017-05-25T12:18:00+00:00

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 
    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: Amit Pundir 
Signed-off-by: Greg Kroah-Hartman

tty: delete non-required instances of include

2014-01-08T01:05:21+00:00

None of these files are actually using any __init type directives
and hence don't need to include .  Most are just a
left over from __devinit and __cpuinit removal, or simply due to
code getting copied from one driver to the next.

Signed-off-by: Paul Gortmaker 
Signed-off-by: Greg Kroah-Hartman

tty: Convert termios_mutex to termios_rwsem

2013-07-23T23:43:01+00:00

termios is commonly accessed unsafely (especially by N_TTY)
because the existing mutex forces exclusive access.
Convert existing usage.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

tty: Don't change receive_room for ioctl(TIOCSETD)

2013-07-23T23:42:59+00:00

tty_set_ldisc() is guaranteed exclusive use of the line discipline
by tty_ldisc_lock_pair_timeout(); shutting off input by resetting
receive_room is unnecessary.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

tty: Clarify multiple-references comment in TIOCSETD ioctl

2013-07-23T23:38:35+00:00

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

tty: Fix hangup race with TIOCSETD ioctl

2013-07-23T23:38:35+00:00

The hangup may already have happened; check for that state also.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

tty: Clarify ldisc variable

2013-07-23T23:38:35+00:00

Rename o_ldisc to avoid confusion with the ldisc of the
'other' tty.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman

tty: Replace ldisc locking with ldisc_sem

2013-07-23T23:38:34+00:00

Line discipline locking was performed with a combination of
a mutex, a status bit, a count, and a waitqueue -- basically,
a rw semaphore.

Replace the existing combination with an ld_semaphore.

Fixes:
 1) the 'reference acquire after ldisc locked' bug
 2) the over-complicated halt mechanism
 3) lock order wrt. tty_lock()
 4) dropping locks while changing ldisc
 5) previously unidentified deadlock while locking ldisc from
    both linked ttys concurrently
 6) previously unidentified recursive deadlocks

Adds much-needed lockdep diagnostics.

Signed-off-by: Peter Hurley 
Signed-off-by: Greg Kroah-Hartman