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| author |   Yifeng Li <tomli@tomli.me> | 2019-03-05 07:02:49 +0800 |
|---|---|---|
| committer |   Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-03-28 01:28:23 +0900 |
| commit | 75ddbc1fb11efac87b611d48e9802f6fe2bb2163 (patch) | |
| tree | 4910a343069646c6396f8b620c432b87bfa4eddf /drivers/tty/vt | |
| parent | tty/vt: fix write/write race in ioctl(KDSKBSENT) handler (diff) | |
| download | linux-dev-75ddbc1fb11efac87b611d48e9802f6fe2bb2163.tar.xz linux-dev-75ddbc1fb11efac87b611d48e9802f6fe2bb2163.zip | |
tty: vt.c: Fix TIOCL_BLANKSCREEN console blanking if blankinterval == 0
Previously, in the userspace, it was possible to use the "setterm" command
from util-linux to blank the VT console by default, using the following
command.
According to the man page,
> The force option keeps the screen blank even if a key is pressed.
It was implemented by calling TIOCL_BLANKSCREEN.
case BLANKSCREEN:
ioctlarg = TIOCL_BLANKSCREEN;
if (ioctl(STDIN_FILENO, TIOCLINUX, &ioctlarg))
warn(_("cannot force blank"));
break;
However, after Linux 4.12, this command ceased to work anymore, which is
unexpected. By inspecting the kernel source, it shows that the issue was
triggered by the side-effect from commit a4199f5eb809 ("tty: Disable
default console blanking interval").
The console blanking is implemented by function do_blank_screen() in vt.c:
"blank_state" will be initialized to "blank_normal_wait" in con_init() if
AND ONLY IF ("blankinterval" > 0). If "blankinterval" is 0, "blank_state"
will be "blank_off" (== 0), and a call to do_blank_screen() will always
abort, even if a forced blanking is required from the user by calling
TIOCL_BLANKSCREEN, the console won't be blanked.
This behavior is unexpected from a user's point-of-view, since it's not
mentioned in any documentation. The setterm man page suggests it will
always work, and the kernel comments in uapi/linux/tiocl.h says
> /* keep screen blank even if a key is pressed */
> #define TIOCL_BLANKSCREEN 14
To fix it, we simply remove the "blank_state != blank_off" check, as
pointed out by Nicolas Pitre, this check doesn't logically make sense
and it's safe to remove.
Suggested-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Fixes: a4199f5eb809 ("tty: Disable default console blanking interval")
Signed-off-by: Yifeng Li <tomli@tomli.me>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/vt')
| -rw-r--r-- | drivers/tty/vt/vt.c | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index d34984aa646d..721edee50234 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -4178,8 +4178,6 @@ void do_blank_screen(int entering_gfx) return; } - if (blank_state != blank_normal_wait) - return; blank_state = blank_off; /* don't blank graphics */ |