syzbot is reporting general protection fault in do_con_write() [1] caused
by vc->vc_screenbuf == ZERO_SIZE_PTR caused by vc->vc_screenbuf_size == 0
caused by vc->vc_cols == vc->vc_rows == vc->vc_size_row == 0 being passed
to ioctl(FBIOPUT_VSCREENINFO) request on /dev/fb0 , for gotoxy(vc, 0, 0)
from reset_terminal() from vc_init() from vc_allocate() on such console
causes vc->vc_pos == 0x10000000e due to
((unsigned long) ZERO_SIZE_PTR) + -1U * 0 + (-1U << 1).
I don't think that a console with 0 column and/or 0 row makes sense, and
I think that we can reject such bogus arguments in fb_set_var() from
ioctl(FBIOPUT_VSCREENINFO). Regardless, I think that it is safer to also
check vc->vc_screenbuf_size when allocating vc->vc_screenbuf from
vc_allocate() from con_install() from tty_init_dev() from tty_open().
Theoretically, cols and rows can be any range as long as
0 < cols * rows * 2 <= KMALLOC_MAX_SIZE is satisfied (e.g.
cols == 1048576 && rows == 2 is possible) because of
vc->vc_size_row = vc->vc_cols << 1;
vc->vc_screenbuf_size = vc->vc_rows * vc->vc_size_row;
in visual_init() and kzalloc(vc->vc_screenbuf_size) in vc_allocate().
But since vc_do_resize() requires cols <= 32767 and rows <= 32767,
applying 1 <= cols <= 32767 and 1 <= rows <= 32767 requirements to
vc_allocate() will be practically fine. (cols != 0 && rows != 0 is
implicitly checked via screenbuf_size != 0.)
This patch does not touch con_init(), for returning -EINVAL there
does not help when we are not returning -ENOMEM.
[1] https://syzkaller.appspot.com/bug?extid=017265e8553724e514e8
Reported-by: syzbot <[email protected]>
Signed-off-by: Tetsuo Handa <[email protected]>
---
drivers/tty/vt/vt.c | 29 ++++++++++++++++++-----------
1 file changed, 18 insertions(+), 11 deletions(-)
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 48a8199f7845..42d8c67a481f 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1092,10 +1092,19 @@ static const struct tty_port_operations vc_port_ops = {
.destruct = vc_port_destruct,
};
+/*
+ * Change # of rows and columns (0 means unchanged/the size of fg_console)
+ * [this is to be used together with some user program
+ * like resize that changes the hardware videomode]
+ */
+#define VC_MAXCOL (32767)
+#define VC_MAXROW (32767)
+
int vc_allocate(unsigned int currcons) /* return 0 on success */
{
struct vt_notifier_param param;
struct vc_data *vc;
+ int err;
WARN_CONSOLE_UNLOCKED();
@@ -1125,6 +1134,11 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */
if (!*vc->vc_uni_pagedir_loc)
con_set_default_unimap(vc);
+ err = -EINVAL;
+ if (vc->vc_cols > VC_MAXCOL || vc->vc_rows > VC_MAXROW ||
+ vc->vc_screenbuf_size > KMALLOC_MAX_SIZE || !vc->vc_screenbuf_size)
+ goto err_free;
+ err = -ENOMEM;
vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_KERNEL);
if (!vc->vc_screenbuf)
goto err_free;
@@ -1143,7 +1157,7 @@ int vc_allocate(unsigned int currcons) /* return 0 on
success */
visual_deinit(vc);
kfree(vc);
vc_cons[currcons].d = NULL;
- return -ENOMEM;
+ return err;
}
static inline int resize_screen(struct vc_data *vc, int width, int height,
@@ -1158,14 +1172,6 @@ static inline int resize_screen(struct vc_data *vc, int
width, int height,
return err;
}
-/*
- * Change # of rows and columns (0 means unchanged/the size of fg_console)
- * [this is to be used together with some user program
- * like resize that changes the hardware videomode]
- */
-#define VC_RESIZE_MAXCOL (32767)
-#define VC_RESIZE_MAXROW (32767)
-
/**
* vc_do_resize - resizing method for the tty
* @tty: tty being resized
@@ -1201,7 +1207,7 @@ static int vc_do_resize(struct tty_struct *tty, struct
vc_data *vc,
user = vc->vc_resize_user;
vc->vc_resize_user = 0;
- if (cols > VC_RESIZE_MAXCOL || lines > VC_RESIZE_MAXROW)
+ if (cols > VC_MAXCOL || lines > VC_MAXROW)
return -EINVAL;
new_cols = (cols ? cols : vc->vc_cols);
@@ -1212,7 +1218,7 @@ static int vc_do_resize(struct tty_struct *tty, struct
vc_data *vc,
if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
return 0;
- if (new_screen_size > KMALLOC_MAX_SIZE)
+ if (new_screen_size > KMALLOC_MAX_SIZE || !new_screen_size)
return -EINVAL;
newscreen = kzalloc(new_screen_size, GFP_USER);
if (!newscreen)
@@ -3393,6 +3399,7 @@ static int __init con_init(void)
INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
tty_port_init(&vc->port);
visual_init(vc, currcons, 1);
+ /* Assuming vc->vc_{cols,rows,screenbuf_size} are sane here. */
vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
vc_init(vc, vc->vc_rows, vc->vc_cols,
currcons || !vc->vc_sw->con_save_screen);
