linux-toradex.git/drivers/tty/tty_ldisc.c, branch v4.9.121

tty: Use __GFP_NOFAIL for tty_ldisc_get()

2018-05-01T22:13:06+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: Don't call panic() at tty_ldisc_init()

2018-05-01T22:13:05+00:00

commit 903f9db10f18f735e62ba447147b6c434b6af003 upstream.

syzbot is reporting kernel panic [1] triggered by memory allocation failure
at tty_ldisc_get() from tty_ldisc_init(). But since both tty_ldisc_get()
and caller of tty_ldisc_init() can cleanly handle errors, tty_ldisc_init()
does not need to call panic() when tty_ldisc_get() failed.

[1] https://syzkaller.appspot.com/bug?id=883431818e036ae6a9981156a64b821110f39187

Signed-off-by: Tetsuo Handa 
Reported-by: syzbot 
Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

tty: fix data race between tty_init_dev and flush of buf

2018-02-03T16:05:41+00:00

commit b027e2298bd588d6fa36ed2eda97447fb3eac078 upstream.

There can be a race, if receive_buf call comes before
tty initialization completes in n_tty_open and tty->disc_data
may be NULL.

CPU0					CPU1
----					----
 000|n_tty_receive_buf_common()   	n_tty_open()
-001|n_tty_receive_buf2()		tty_ldisc_open.isra.3()
-002|tty_ldisc_receive_buf(inline)	tty_ldisc_setup()

Using ldisc semaphore lock in tty_init_dev till disc_data
initializes completely.

Signed-off-by: Gaurav Kohli 
Reviewed-by: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

tty: fix data race in tty_ldisc_ref_wait()

2017-12-20T09:07:26+00:00

[ Upstream commit a4a3e061149f09c075f108b6f1cf04d9739a6bc2 ]

tty_ldisc_ref_wait() checks tty->ldisc under tty->ldisc_sem.
But if ldisc==NULL it releases them sem and reloads
tty->ldisc without holding the sem. This is wrong and
can lead to returning non-NULL ldisc without protection.

Don't reload tty->ldisc second time.

Signed-off-by: Dmitry Vyukov 
Cc: syzkaller@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: Peter Hurley 
Cc: One Thousand Gnomes 
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

tty: don't panic on OOM in tty_set_ldisc()

2017-12-20T09:07:25+00:00

[ Upstream commit 5362544bebe85071188dd9e479b5a5040841c895 ]

If tty_ldisc_open() fails in tty_set_ldisc(), it tries to go back
to the old discipline or N_TTY. But that can fail as well, in such
case it panics. This is not a graceful way to handle OOM.

Leave ldisc==NULL if all attempts fail instead.
Also use existing tty_ldisc_reinit() helper function instead of
tty_ldisc_restore(). Also don't WARN/BUG in tty_ldisc_reinit()
if N_TTY fails, which would have the same net effect of bringing
kernel down on OOM. Instead print a single line message about
what has happened.

Signed-off-by: Dmitry Vyukov 
Cc: syzkaller@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: Peter Hurley 
Cc: One Thousand Gnomes 
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

tty: Eliminate global symbol tty_ldisc_N_TTY

2016-01-27T23:13:28+00:00

Reduce global tty symbols; move and rename tty_ldisc_begin() as
n_tty_init() and redefine the N_TTY ldisc ops as file scope.

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

tty: Avoid unnecessary temporaries for tty->ldisc

2016-01-27T23:01:44+00:00

tty_ldisc_setup() is race-free and can reference tty->ldisc without
snapshots.

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

tty: Destroy ldisc instance on hangup

2016-01-27T23:01:44+00:00

Currently, when the tty is hungup, the ldisc is re-instanced; ie., the
current instance is destroyed and a new instance is created. The purpose
of this design was to guarantee a valid, open ldisc for the lifetime of
the tty.

However, now that tty buffers are owned by and have lifetime equivalent
to the tty_port (since v3.10), any data received immediately after the
ldisc is re-instanced may cause continued driver i/o operations
concurrently with the driver's hangup() operation. For drivers that
shutdown h/w on hangup, this is unexpected and usually bad. For example,
the serial core may free the xmit buffer page concurrently with an
in-progress write() operation (triggered by echo).

With the existing stable and robust ldisc reference handling, the
cleaned-up tty_reopen(), the straggling unsafe ldisc use cleaned up, and
the preparation to properly handle a NULL tty->ldisc, the ldisc instance
can be destroyed and only re-instanced when the tty is re-opened.

If the tty was opened as /dev/console or /dev/tty0, the original behavior
of re-instancing the ldisc is retained (the 'reinit' parameter to
tty_ldisc_hangup() is true). This is required since those file descriptors
are never hungup.

This patch has neglible impact on userspace; the tty file_operations ptr
is changed to point to the hungup file operations _before_ the ldisc
instance is destroyed, so only racing file operations might now retrieve
a NULL ldisc reference (which is simply handled as if the hungup file
operation had been called instead -- see "tty: Prepare for destroying
line discipline on hangup").

This resolves a long-standing FIXME and several crash reports.

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

tty: Refactor tty_ldisc_reinit() for reuse

2016-01-27T23:01:44+00:00

At tty hangup, the line discipline instance is reinitialized by
closing the current ldisc instance and opening a new instance.
This operation is complicated by error recovery: if the attempt
to reinit the current line discipline fails, the line discipline
is reset to N_TTY (which should not but can fail).

Re-purpose tty_ldisc_reinit() to return a valid, open line discipline
instance, or otherwise, an error.

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

tty: Use 'disc' for line discipline index name

2016-01-27T23:01:44+00:00

tty->ldisc is a ptr to struct tty_ldisc, but unfortunately 'ldisc' is
also used as a parameter or local name to refer to the line discipline
index value (ie, N_TTY, N_GSM, etc.); instead prefer the name used
by the line discipline registration/ref counting functions.

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