linux-kernel - [PATCH 5.6 136/167] vt: dont hardcode the mem allocation upper bound

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Message-Id: <20200428182242.697621873@linuxfoundation.org>
Date:   Tue, 28 Apr 2020 20:25:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nicolas Pitre <nico@...xnic.net>
Subject: [PATCH 5.6 136/167] vt: dont hardcode the mem allocation upper bound

From: Nicolas Pitre <nico@...xnic.net>

commit 2717769e204e83e65b8819c5e2ef3e5b6639b270 upstream.

The code in vc_do_resize() bounds the memory allocation size to avoid
exceeding MAX_ORDER down the kzalloc() call chain and generating a
runtime warning triggerable from user space. However, not only is it
unwise to use a literal value here, but MAX_ORDER may also be
configurable based on CONFIG_FORCE_MAX_ZONEORDER.
Let's use KMALLOC_MAX_SIZE instead.

Note that prior commit bb1107f7c605 ("mm, slab: make sure that
KMALLOC_MAX_SIZE will fit into MAX_ORDER") the KMALLOC_MAX_SIZE value
could not be relied upon.

Signed-off-by: Nicolas Pitre <nico@...xnic.net>
Cc: <stable@...r.kernel.org> # v4.10+
Link: https://lore.kernel.org/r/nycvar.YSQ.7.76.2003281702410.2671@knanqh.ubzr
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/vt/vt.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1206,7 +1206,7 @@ static int vc_do_resize(struct tty_struc
 	if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
 		return 0;

-	if (new_screen_size > (4 << 20))
+	if (new_screen_size > KMALLOC_MAX_SIZE)
 		return -EINVAL;
 	newscreen = kzalloc(new_screen_size, GFP_USER);
 	if (!newscreen)