linux-kernel - [PATCH] vt: vt_ioctl: remove unnecessary console allocation checks

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Date:   Mon, 24 Feb 2020 00:03:26 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] vt: vt_ioctl: remove unnecessary console allocation checks

From: Eric Biggers <ebiggers@...gle.com>

The vc_cons_allocated() checks in vt_ioctl() and vt_compat_ioctl() are
unnecessary because they can only be reached by calling ioctl() on an
open tty, which implies the corresponding virtual console is allocated.

And even if the virtual console *could* be freed concurrently, then
these checks would be broken since they aren't done under console_lock,
and the vc_data is dereferenced before them anyway.

So, remove these unneeded checks to avoid confusion.

Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 drivers/tty/vt/vt_ioctl.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
index 57d681706fa85..400000a8830a1 100644
--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -339,22 +339,13 @@ int vt_ioctl(struct tty_struct *tty,
 {
 	struct vc_data *vc = tty->driver_data;
 	struct console_font_op op;	/* used in multiple places here */
-	unsigned int console;
+	unsigned int console = vc->vc_num;
 	unsigned char ucval;
 	unsigned int uival;
 	void __user *up = (void __user *)arg;
 	int i, perm;
 	int ret = 0;
 
-	console = vc->vc_num;
-
-
-	if (!vc_cons_allocated(console)) { 	/* impossible? */
-		ret = -ENOIOCTLCMD;
-		goto out;
-	}
-
-
 	/*
 	 * To have permissions to do most of the vt ioctls, we either have
 	 * to be the owner of the tty, or have CAP_SYS_TTY_CONFIG.
@@ -1184,14 +1175,9 @@ long vt_compat_ioctl(struct tty_struct *tty,
 {
 	struct vc_data *vc = tty->driver_data;
 	struct console_font_op op;	/* used in multiple places here */
-	unsigned int console = vc->vc_num;
 	void __user *up = compat_ptr(arg);
 	int perm;
 
-
-	if (!vc_cons_allocated(console)) 	/* impossible? */
-		return -ENOIOCTLCMD;
-
 	/*
 	 * To have permissions to do most of the vt ioctls, we either have
 	 * to be the owner of the tty, or have CAP_SYS_TTY_CONFIG.
-- 
2.25.1