vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console
The VT_DISALLOCATE ioctl can free a virtual console while tty_release()
is still running, causing a use-after-free in con_shutdown(). This
occurs because VT_DISALLOCATE considers a virtual console's
'struct vc_data' to be unused as soon as the corresponding tty's
refcount hits 0. But actually it may be still being closed.
Fix this by making vc_data be reference-counted via the embedded
'struct tty_port'. A newly allocated virtual console has refcount 1.
Opening it for the first time increments the refcount to 2. Closing it
for the last time decrements the refcount (in tty_operations::cleanup()
so that it happens late enough), as does VT_DISALLOCATE.
Reproducer:
#include <fcntl.h>
#include <linux/vt.h>
#include <sys/ioctl.h>
#include <unistd.h>
int main()
{
if (fork()) {
for (;;)
close(open("/dev/tty5", O_RDWR));
} else {
int fd = open("/dev/tty10", O_RDWR);
for (;;)
ioctl(fd, VT_DISALLOCATE, 5);
}
}
KASAN report:
BUG: KASAN: use-after-free in con_shutdown+0x76/0x80 drivers/tty/vt/vt.c:3278
Write of size 8 at addr ffff88806a4ec108 by task syz_vt/129
CPU: 0 PID: 129 Comm: syz_vt Not tainted 5.6.0-rc2 #11
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20191223_100556-anatol 04/01/2014
Call Trace:
[...]
con_shutdown+0x76/0x80 drivers/tty/vt/vt.c:3278
release_tty+0xa8/0x410 drivers/tty/tty_io.c:1514
tty_release_struct+0x34/0x50 drivers/tty/tty_io.c:1629
tty_release+0x984/0xed0 drivers/tty/tty_io.c:1789
[...]
Allocated by task 129:
[...]
kzalloc include/linux/slab.h:669 [inline]
vc_allocate drivers/tty/vt/vt.c:1085 [inline]
vc_allocate+0x1ac/0x680 drivers/tty/vt/vt.c:1066
con_install+0x4d/0x3f0 drivers/tty/vt/vt.c:3229
tty_driver_install_tty drivers/tty/tty_io.c:1228 [inline]
tty_init_dev+0x94/0x350 drivers/tty/tty_io.c:1341
tty_open_by_driver drivers/tty/tty_io.c:1987 [inline]
tty_open+0x3ca/0xb30 drivers/tty/tty_io.c:2035
[...]
Freed by task 130:
[...]
kfree+0xbf/0x1e0 mm/slab.c:3757
vt_disallocate drivers/tty/vt/vt_ioctl.c:300 [inline]
vt_ioctl+0x16dc/0x1e30 drivers/tty/vt/vt_ioctl.c:818
tty_ioctl+0x9db/0x11b0 drivers/tty/tty_io.c:2660
[...]
Fixes: 4001d7b7fc
("vt: push down the tty lock so we can see what is left to tackle")
Cc: <stable@vger.kernel.org> # v3.4+
Reported-by: syzbot+522643ab5729b0421998@syzkaller.appspotmail.com
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20200322034305.210082-2-ebiggers@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
3b9c55efb2
commit
ca4463bf84
|
@ -1075,6 +1075,17 @@ static void visual_deinit(struct vc_data *vc)
|
||||||
module_put(vc->vc_sw->owner);
|
module_put(vc->vc_sw->owner);
|
||||||
}
|
}
|
||||||
|
|
||||||
|
static void vc_port_destruct(struct tty_port *port)
|
||||||
|
{
|
||||||
|
struct vc_data *vc = container_of(port, struct vc_data, port);
|
||||||
|
|
||||||
|
kfree(vc);
|
||||||
|
}
|
||||||
|
|
||||||
|
static const struct tty_port_operations vc_port_ops = {
|
||||||
|
.destruct = vc_port_destruct,
|
||||||
|
};
|
||||||
|
|
||||||
int vc_allocate(unsigned int currcons) /* return 0 on success */
|
int vc_allocate(unsigned int currcons) /* return 0 on success */
|
||||||
{
|
{
|
||||||
struct vt_notifier_param param;
|
struct vt_notifier_param param;
|
||||||
|
@ -1100,6 +1111,7 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */
|
||||||
|
|
||||||
vc_cons[currcons].d = vc;
|
vc_cons[currcons].d = vc;
|
||||||
tty_port_init(&vc->port);
|
tty_port_init(&vc->port);
|
||||||
|
vc->port.ops = &vc_port_ops;
|
||||||
INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
|
INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
|
||||||
|
|
||||||
visual_init(vc, currcons, 1);
|
visual_init(vc, currcons, 1);
|
||||||
|
@ -3250,6 +3262,7 @@ static int con_install(struct tty_driver *driver, struct tty_struct *tty)
|
||||||
|
|
||||||
tty->driver_data = vc;
|
tty->driver_data = vc;
|
||||||
vc->port.tty = tty;
|
vc->port.tty = tty;
|
||||||
|
tty_port_get(&vc->port);
|
||||||
|
|
||||||
if (!tty->winsize.ws_row && !tty->winsize.ws_col) {
|
if (!tty->winsize.ws_row && !tty->winsize.ws_col) {
|
||||||
tty->winsize.ws_row = vc_cons[currcons].d->vc_rows;
|
tty->winsize.ws_row = vc_cons[currcons].d->vc_rows;
|
||||||
|
@ -3285,6 +3298,13 @@ static void con_shutdown(struct tty_struct *tty)
|
||||||
console_unlock();
|
console_unlock();
|
||||||
}
|
}
|
||||||
|
|
||||||
|
static void con_cleanup(struct tty_struct *tty)
|
||||||
|
{
|
||||||
|
struct vc_data *vc = tty->driver_data;
|
||||||
|
|
||||||
|
tty_port_put(&vc->port);
|
||||||
|
}
|
||||||
|
|
||||||
static int default_color = 7; /* white */
|
static int default_color = 7; /* white */
|
||||||
static int default_italic_color = 2; // green (ASCII)
|
static int default_italic_color = 2; // green (ASCII)
|
||||||
static int default_underline_color = 3; // cyan (ASCII)
|
static int default_underline_color = 3; // cyan (ASCII)
|
||||||
|
@ -3410,7 +3430,8 @@ static const struct tty_operations con_ops = {
|
||||||
.throttle = con_throttle,
|
.throttle = con_throttle,
|
||||||
.unthrottle = con_unthrottle,
|
.unthrottle = con_unthrottle,
|
||||||
.resize = vt_resize,
|
.resize = vt_resize,
|
||||||
.shutdown = con_shutdown
|
.shutdown = con_shutdown,
|
||||||
|
.cleanup = con_cleanup,
|
||||||
};
|
};
|
||||||
|
|
||||||
static struct cdev vc0_cdev;
|
static struct cdev vc0_cdev;
|
||||||
|
|
|
@ -310,10 +310,8 @@ static int vt_disallocate(unsigned int vc_num)
|
||||||
vc = vc_deallocate(vc_num);
|
vc = vc_deallocate(vc_num);
|
||||||
console_unlock();
|
console_unlock();
|
||||||
|
|
||||||
if (vc && vc_num >= MIN_NR_CONSOLES) {
|
if (vc && vc_num >= MIN_NR_CONSOLES)
|
||||||
tty_port_destroy(&vc->port);
|
tty_port_put(&vc->port);
|
||||||
kfree(vc);
|
|
||||||
}
|
|
||||||
|
|
||||||
return ret;
|
return ret;
|
||||||
}
|
}
|
||||||
|
@ -333,10 +331,8 @@ static void vt_disallocate_all(void)
|
||||||
console_unlock();
|
console_unlock();
|
||||||
|
|
||||||
for (i = 1; i < MAX_NR_CONSOLES; i++) {
|
for (i = 1; i < MAX_NR_CONSOLES; i++) {
|
||||||
if (vc[i] && i >= MIN_NR_CONSOLES) {
|
if (vc[i] && i >= MIN_NR_CONSOLES)
|
||||||
tty_port_destroy(&vc[i]->port);
|
tty_port_put(&vc[i]->port);
|
||||||
kfree(vc[i]);
|
|
||||||
}
|
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
|
Loading…
Reference in New Issue