linux-stable.git/drivers/tty/vt/selection.c, branch v5.7

vt: selection, use rounddown() for start/endline computation

2020-03-16T07:41:17+00:00

We have a helper called rounddown for these modulo computations. So use
it.

No functional change intended and "objdump -d" proves that.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20200316065911.11024-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, fix double lock introduced by a merge

2020-03-16T07:39:47+00:00

The merge commit cb05c6c82fb0 (Merge 5.6-rc5 into tty-next) introduced a
double lock to set_selection_kernel. vc_sel.lock is locked both in
set_selection_kernel and its callee __set_selection_kernel now.

Remove the latter.

Signed-off-by: Jiri Slaby 
Cc: Stephen Rothwell 
Link: https://lore.kernel.org/r/20200316064544.4799-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

Merge 5.6-rc5 into tty-next

2020-03-10T09:02:49+00:00

We need the vt fixes in here and it resolves a merge issue with
drivers/tty/vt/selection.c

Reported-by: Stephen Rothwell 
Signed-off-by: Greg Kroah-Hartman

vt: selection, indent switch-case properly

2020-03-06T07:35:40+00:00

Shift the cases one level left as this is how we are supposed to write
the switch-case code according to the CodingStyle.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20200219073951.16151-9-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, remove redeclaration of poke_blanked_console

2020-03-06T07:35:40+00:00

It is declared in vt_kern.h, so no need to declare it in selection.c
which includes the header.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20200219073951.16151-8-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, create struct from console selection globals

2020-03-06T07:35:39+00:00

Move all the selection global variables to a structure vc_selection,
instantiated as vc_sel. This helps to group all the variables together
and see what should be protected by the embedded lock too.

It might be used later also for per-console selection support.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20200219073951.16151-5-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, localize use_unicode

2020-03-06T07:35:38+00:00

use_unicode needs not be global. It is used only in set_selection_kernel
and sel_pos (a callee). It is also always set there prior calling
sel_pos. So make use_unicode local and rename it to plain shorter
"unicode". Finally, propagate it to sel_pos via parameter.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20200219073951.16151-4-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, remove 2 local variables from set_selection_kernel

2020-03-06T07:35:38+00:00

multiplier and mode are not actually needed:
* multiplier is used only in kmalloc_array, so use "use_unicode ? 4 : 1"
  directly
* mode is used only to assign a bool in this manner:
  if (cond)
    x = true;
  else
    x = false;
  So do "x = cond" directly.

Signed-off-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20200219073951.16151-3-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, push sel_lock up

2020-02-28T15:06:49+00:00

sel_lock cannot nest in the console lock. Thanks to syzkaller, the
kernel states firmly:

> WARNING: possible circular locking dependency detected
> 5.6.0-rc3-syzkaller #0 Not tainted
> ------------------------------------------------------
> syz-executor.4/20336 is trying to acquire lock:
> ffff8880a2e952a0 (&tty->termios_rwsem){++++}, at: tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136
>
> but task is already holding lock:
> ffffffff89462e70 (sel_lock){+.+.}, at: paste_selection+0x118/0x470 drivers/tty/vt/selection.c:374
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #2 (sel_lock){+.+.}:
>        mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118
>        set_selection_kernel+0x3b8/0x18a0 drivers/tty/vt/selection.c:217
>        set_selection_user+0x63/0x80 drivers/tty/vt/selection.c:181
>        tioclinux+0x103/0x530 drivers/tty/vt/vt.c:3050
>        vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364

This is ioctl(TIOCL_SETSEL).
Locks held on the path: console_lock -> sel_lock

> -> #1 (console_lock){+.+.}:
>        console_lock+0x46/0x70 kernel/printk/printk.c:2289
>        con_flush_chars+0x50/0x650 drivers/tty/vt/vt.c:3223
>        n_tty_write+0xeae/0x1200 drivers/tty/n_tty.c:2350
>        do_tty_write drivers/tty/tty_io.c:962 [inline]
>        tty_write+0x5a1/0x950 drivers/tty/tty_io.c:1046

This is write().
Locks held on the path: termios_rwsem -> console_lock

> -> #0 (&tty->termios_rwsem){++++}:
>        down_write+0x57/0x140 kernel/locking/rwsem.c:1534
>        tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136
>        mkiss_receive_buf+0x12aa/0x1340 drivers/net/hamradio/mkiss.c:902
>        tty_ldisc_receive_buf+0x12f/0x170 drivers/tty/tty_buffer.c:465
>        paste_selection+0x346/0x470 drivers/tty/vt/selection.c:389
>        tioclinux+0x121/0x530 drivers/tty/vt/vt.c:3055
>        vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364

This is ioctl(TIOCL_PASTESEL).
Locks held on the path: sel_lock -> termios_rwsem

> other info that might help us debug this:
>
> Chain exists of:
>   &tty->termios_rwsem --> console_lock --> sel_lock

Clearly. From the above, we have:
 console_lock -> sel_lock
 sel_lock -> termios_rwsem
 termios_rwsem -> console_lock

Fix this by reversing the console_lock -> sel_lock dependency in
ioctl(TIOCL_SETSEL). First, lock sel_lock, then console_lock.

Signed-off-by: Jiri Slaby 
Reported-by: syzbot+26183d9746e62da329b8@syzkaller.appspotmail.com
Fixes: 07e6124a1a46 ("vt: selection, close sel_buffer race")
Cc: stable 
Link: https://lore.kernel.org/r/20200228115406.5735-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman

vt: selection, push console lock down

2020-02-28T15:06:49+00:00

We need to nest the console lock in sel_lock, so we have to push it down
a bit. Fortunately, the callers of set_selection_* just lock the console
lock around the function call. So moving it down is easy.

In the next patch, we switch the order.

Signed-off-by: Jiri Slaby 
Fixes: 07e6124a1a46 ("vt: selection, close sel_buffer race")
Cc: stable 
Link: https://lore.kernel.org/r/20200228115406.5735-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman