[PATCH 1/2] ipack: ipoctal: fix UAF, null-ptr-deref, and use-after-free in cleanup on remove
From: Pei Xiao
Date: Thu Jun 25 2026 - 22:32:22 EST
Three issues arise when the device is removed while a tty session is
still active:
1. UAF of struct ipoctal: the remove callback frees ipoctal via
kfree() while tty ops may still access it. Fix by introducing
kref-based lifetime management — kref is taken in install() when
a tty is opened and released in cleanup() when the tty is finally
destroyed; remove() uses kref_put() instead of kfree().
2. NULL dereference in ipoctal_write_tty(): __ipoctal_remove()
frees xmit_buf via tty_port_free_xmit_buf() while a userspace
process may still hold the tty fd and call write(). Fix by
checking for NULL xmit_buf in ipoctal_write_tty().
3. UAF in ipoctal_cleanup(): ipack_put_carrier(ipoctal->dev)
dereferences ipoctal->dev after the ipack_device has been freed
by ipack_device_del(). Fix by caching ipoctal->carrier_owner
during probe() and calling module_put() on the cached pointer
directly in cleanup(), avoiding any access to ipoctal->dev.
Also introduce a "removed" flag in struct ipoctal, set at the start
of __ipoctal_remove(), and checked in every tty op that accesses
hardware resources (port_activate, write_tty, set_termios, hangup,
shutdown). This prevents page faults when devm_ioremap() regions
are unmapped after remove() returns.
Reported-by: Shuangpeng Bai <shuangpeng.kernel@xxxxxxxxx>
Closes: https://lore.kernel.org/lkml/178144969601.60470.1257088106279546587@xxxxxxxxx/
Fixes: 05e5027efc9c ("Staging: ipack: move out of staging")
Signed-off-by: Pei Xiao <xiaopei01@xxxxxxxxxx>
---
drivers/ipack/devices/ipoctal.c | 56 ++++++++++++++++++++++++++++++---
1 file changed, 52 insertions(+), 4 deletions(-)
diff --git a/drivers/ipack/devices/ipoctal.c b/drivers/ipack/devices/ipoctal.c
index 1bbefc6de708..bf71b8952a7c 100644
--- a/drivers/ipack/devices/ipoctal.c
+++ b/drivers/ipack/devices/ipoctal.c
@@ -10,6 +10,7 @@
#include <linux/device.h>
#include <linux/module.h>
#include <linux/interrupt.h>
+#include <linux/kref.h>
#include <linux/sched.h>
#include <linux/tty.h>
#include <linux/serial.h>
@@ -25,6 +26,8 @@
static const struct tty_operations ipoctal_fops;
+static void ipoctal_release(struct kref *kref);
+
struct ipoctal_channel {
struct ipoctal_stats stats;
unsigned int nb_bytes;
@@ -49,6 +52,9 @@ struct ipoctal {
struct tty_driver *tty_drv;
u8 __iomem *mem8_space;
u8 __iomem *int_space;
+ struct kref kref;
+ struct module *carrier_owner;
+ bool removed;
};
static inline struct ipoctal *chan_to_ipoctal(struct ipoctal_channel *chan,
@@ -70,8 +76,14 @@ static void ipoctal_reset_channel(struct ipoctal_channel *channel)
static int ipoctal_port_activate(struct tty_port *port, struct tty_struct *tty)
{
struct ipoctal_channel *channel;
+ struct ipoctal *ipoctal;
channel = dev_get_drvdata(tty->dev);
+ ipoctal = chan_to_ipoctal(channel, tty->index);
+
+
+ if (ipoctal->removed)
+ return -ENODEV;
/*
* Enable RX. TX will be enabled when
@@ -95,6 +107,7 @@ static int ipoctal_install(struct tty_driver *driver, struct tty_struct *tty)
if (res)
goto err_put_carrier;
+ kref_get(&ipoctal->kref);
tty->driver_data = channel;
return 0;
@@ -460,8 +473,13 @@ static ssize_t ipoctal_write_tty(struct tty_struct *tty, const u8 *buf,
size_t count)
{
struct ipoctal_channel *channel = tty->driver_data;
+ struct ipoctal *ipoctal = chan_to_ipoctal(channel, tty->index);
size_t char_copied;
+
+ if (ipoctal->removed || !channel->tty_port.xmit_buf)
+ return 0;
+
char_copied = ipoctal_copy_write_buffer(channel, buf, count);
/* As the IP-OCTAL 485 only supports half duplex, do it manually */
@@ -501,8 +519,13 @@ static void ipoctal_set_termios(struct tty_struct *tty,
unsigned char mr2 = 0;
unsigned char csr = 0;
struct ipoctal_channel *channel = tty->driver_data;
+ struct ipoctal *ipoctal = chan_to_ipoctal(channel, tty->index);
speed_t baud;
+
+ if (ipoctal->removed)
+ return;
+
cflag = tty->termios.c_cflag;
/* Disable and reset everything before change the setup */
@@ -631,10 +654,16 @@ static void ipoctal_hangup(struct tty_struct *tty)
{
unsigned long flags;
struct ipoctal_channel *channel = tty->driver_data;
+ struct ipoctal *ipoctal;
if (channel == NULL)
return;
+ ipoctal = chan_to_ipoctal(channel, tty->index);
+
+ if (ipoctal->removed)
+ return;
+
spin_lock_irqsave(&channel->lock, flags);
channel->nb_bytes = 0;
channel->pointer_read = 0;
@@ -651,10 +680,16 @@ static void ipoctal_hangup(struct tty_struct *tty)
static void ipoctal_shutdown(struct tty_struct *tty)
{
struct ipoctal_channel *channel = tty->driver_data;
+ struct ipoctal *ipoctal;
if (channel == NULL)
return;
+ ipoctal = chan_to_ipoctal(channel, tty->index);
+
+ if (ipoctal->removed)
+ return;
+
ipoctal_reset_channel(channel);
tty_port_set_initialized(&channel->tty_port, false);
}
@@ -664,8 +699,9 @@ static void ipoctal_cleanup(struct tty_struct *tty)
struct ipoctal_channel *channel = tty->driver_data;
struct ipoctal *ipoctal = chan_to_ipoctal(channel, tty->index);
- /* release the carrier driver */
- ipack_put_carrier(ipoctal->dev);
+ /* release the carrier driver via cached owner */
+ module_put(ipoctal->carrier_owner);
+ kref_put(&ipoctal->kref, ipoctal_release);
}
static const struct tty_operations ipoctal_fops = {
@@ -683,6 +719,13 @@ static const struct tty_operations ipoctal_fops = {
.cleanup = ipoctal_cleanup,
};
+static void ipoctal_release(struct kref *kref)
+{
+ struct ipoctal *ipoctal = container_of(kref, struct ipoctal, kref);
+
+ kfree(ipoctal);
+}
+
static int ipoctal_probe(struct ipack_device *dev)
{
int res;
@@ -692,7 +735,10 @@ static int ipoctal_probe(struct ipack_device *dev)
if (ipoctal == NULL)
return -ENOMEM;
+ kref_init(&ipoctal->kref);
+
ipoctal->dev = dev;
+ ipoctal->carrier_owner = dev->bus->owner;
res = ipoctal_inst_slot(ipoctal, dev->bus->bus_nr, dev->slot);
if (res)
goto out_uninst;
@@ -701,7 +747,7 @@ static int ipoctal_probe(struct ipack_device *dev)
return 0;
out_uninst:
- kfree(ipoctal);
+ kref_put(&ipoctal->kref, ipoctal_release);
return res;
}
@@ -709,6 +755,8 @@ static void __ipoctal_remove(struct ipoctal *ipoctal)
{
int i;
+ ipoctal->removed = true;
+
ipoctal->dev->bus->ops->free_irq(ipoctal->dev);
for (i = 0; i < NR_CHANNELS; i++) {
@@ -725,7 +773,7 @@ static void __ipoctal_remove(struct ipoctal *ipoctal)
tty_unregister_driver(ipoctal->tty_drv);
kfree(ipoctal->tty_drv->name);
tty_driver_kref_put(ipoctal->tty_drv);
- kfree(ipoctal);
+ kref_put(&ipoctal->kref, ipoctal_release);
}
static void ipoctal_remove(struct ipack_device *idev)
--
2.25.1