On a board running ntpd and gpsd, I'm seeing a consistent use-after-free
in sys_exit() from gpsd when rebooting:
pps pps1: removed
------------[ cut here ]------------
kobject: '(null)' (00000000db4bec24): is not initialized, yet kobject_put() is being called.
WARNING: CPU: 2 PID: 440 at lib/kobject.c:734 kobject_put+0x120/0x150
CPU: 2 UID: 299 PID: 440 Comm: gpsd Not tainted 6.11.0-rc6-00308-gb31c44928842 #1
Hardware name: Raspberry Pi 4 Model B Rev 1.1 (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : kobject_put+0x120/0x150
lr : kobject_put+0x120/0x150
sp : ffffffc0803d3ae0
x29: ffffffc0803d3ae0 x28: ffffff8042dc9738 x27: 0000000000000001
x26: 0000000000000000 x25: ffffff8042dc9040 x24: ffffff8042dc9440
x23: ffffff80402a4620 x22: ffffff8042ef4bd0 x21: ffffff80405cb600
x20: 000000000008001b x19: ffffff8040b3b6e0 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 696e6920746f6e20
x14: 7369203a29343263 x13: 205d303434542020 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
kobject_put+0x120/0x150
cdev_put+0x20/0x3c
__fput+0x2c4/0x2d8
____fput+0x1c/0x38
task_work_run+0x70/0xfc
do_exit+0x2a0/0x924
do_group_exit+0x34/0x90
get_signal+0x7fc/0x8c0
do_signal+0x128/0x13b4
do_notify_resume+0xdc/0x160
el0_svc+0xd4/0xf8
el0t_64_sync_handler+0x140/0x14c
el0t_64_sync+0x190/0x194
---[ end trace 0000000000000000 ]---
...followed by more symptoms of corruption, with similar stacks:
refcount_t: underflow; use-after-free.
kernel BUG at lib/list_debug.c:62!
Kernel panic - not syncing: Oops - BUG: Fatal exception
This happens because pps_device_destruct() frees the pps_device with the
embedded cdev immediately after calling cdev_del(), but, as the comment
above cdev_del() notes, fops for previously opened cdevs are still
callable even after cdev_del() returns. I think this bug has always
been there: I can't explain why it suddenly started happening every time
I reboot this particular board.
In commit d953e0e837e6 ("pps: Fix a use-after free bug when
unregistering a source."), George Spelvin suggested removing the
embedded cdev. That seems like the simplest way to fix this, so I've
implemented his suggestion, using __register_chrdev() with pps_idr
becoming the source of truth for which minor corresponds to which
device.
But now that pps_idr defines userspace visibility instead of cdev_add(),
we need to be sure the pps->dev refcount can't reach zero while
userspace can still find it again. So, the idr_remove() call moves to
pps_unregister_cdev(), and pps_idr now holds a reference to pps->dev.
pps_core: source serial1 got cdev (251:1)
<...>
pps pps1: removed
pps_core: unregistering pps1
pps_core: deallocating pps1
Fixes: d953e0e837e6 ("pps: Fix a use-after free bug when unregistering a source.")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Calvin Owens <calvin@xxxxxxxxxx>
---
Changes in v3:
- Shorten patch title
- Embed the device struct in the pps struct
- Use foo_device(&pps->dev) instead of kobject_foo(&pps->dev.kobj)
Changes in v2:
- Don't move pr_debug() from pps_device_destruct() to pps_unregister_cdev()
- Actually add stable@xxxxxxxxxxxxxxx to CC
---
drivers/pps/clients/pps-gpio.c | 2 +-
drivers/pps/clients/pps-ktimer.c | 4 +-
drivers/pps/clients/pps-ldisc.c | 6 +-
drivers/pps/clients/pps_parport.c | 4 +-
drivers/pps/kapi.c | 10 +--
drivers/pps/kc.c | 10 +--
drivers/pps/pps.c | 127 ++++++++++++++++--------------
include/linux/pps_kernel.h | 3 +-
8 files changed, 85 insertions(+), 81 deletions(-)
diff --git a/drivers/pps/clients/pps-gpio.c b/drivers/pps/clients/pps-gpio.c
index 791fdc9326dd..a21bf56e7a87 100644
--- a/drivers/pps/clients/pps-gpio.c
+++ b/drivers/pps/clients/pps-gpio.c
@@ -214,7 +214,7 @@ static int pps_gpio_probe(struct platform_device *pdev)
return -EINVAL;
}
- dev_info(data->pps->dev, "Registered IRQ %d as PPS source\n",
+ dev_info(&data->pps->dev, "Registered IRQ %d as PPS source\n",
data->irq);
return 0;
diff --git a/drivers/pps/clients/pps-ktimer.c b/drivers/pps/clients/pps-ktimer.c
index d33106bd7a29..00cf406377a1 100644
--- a/drivers/pps/clients/pps-ktimer.c
+++ b/drivers/pps/clients/pps-ktimer.c
@@ -56,7 +56,7 @@ static struct pps_source_info pps_ktimer_info = {
static void __exit pps_ktimer_exit(void)
{
- dev_info(pps->dev, "ktimer PPS source unregistered\n");
+ dev_info(&pps->dev, "ktimer PPS source unregistered\n");
del_timer_sync(&ktimer);
pps_unregister_source(pps);
@@ -74,7 +74,7 @@ static int __init pps_ktimer_init(void)
timer_setup(&ktimer, pps_ktimer_event, 0);
mod_timer(&ktimer, jiffies + HZ);
- dev_info(pps->dev, "ktimer PPS source registered\n");
+ dev_info(&pps->dev, "ktimer PPS source registered\n");
return 0;
}
diff --git a/drivers/pps/clients/pps-ldisc.c b/drivers/pps/clients/pps-ldisc.c
index 443d6bae19d1..49ae33cca03d 100644
--- a/drivers/pps/clients/pps-ldisc.c
+++ b/drivers/pps/clients/pps-ldisc.c
@@ -32,7 +32,7 @@ static void pps_tty_dcd_change(struct tty_struct *tty, bool active)
pps_event(pps, &ts, active ? PPS_CAPTUREASSERT :
PPS_CAPTURECLEAR, NULL);
- dev_dbg(pps->dev, "PPS %s at %lu\n",
+ dev_dbg(&pps->dev, "PPS %s at %lu\n",
active ? "assert" : "clear", jiffies);
}
@@ -69,7 +69,7 @@ static int pps_tty_open(struct tty_struct *tty)
goto err_unregister;
}
- dev_info(pps->dev, "source \"%s\" added\n", info.path);
+ dev_info(&pps->dev, "source \"%s\" added\n", info.path);
return 0;
@@ -89,7 +89,7 @@ static void pps_tty_close(struct tty_struct *tty)
if (WARN_ON(!pps))
return;
- dev_info(pps->dev, "removed\n");
+ dev_info(&pps->dev, "removed\n");
pps_unregister_source(pps);
}
diff --git a/drivers/pps/clients/pps_parport.c b/drivers/pps/clients/pps_parport.c
index abaffb4e1c1c..24db06750297 100644
--- a/drivers/pps/clients/pps_parport.c
+++ b/drivers/pps/clients/pps_parport.c
@@ -81,7 +81,7 @@ static void parport_irq(void *handle)
/* check the signal (no signal means the pulse is lost this time) */
if (!signal_is_set(port)) {
local_irq_restore(flags);
- dev_err(dev->pps->dev, "lost the signal\n");
+ dev_err(&dev->pps->dev, "lost the signal\n");
goto out_assert;
}
@@ -98,7 +98,7 @@ static void parport_irq(void *handle)
/* timeout */
dev->cw_err++;
if (dev->cw_err >= CLEAR_WAIT_MAX_ERRORS) {
- dev_err(dev->pps->dev, "disabled clear edge capture after %d"
+ dev_err(&dev->pps->dev, "disabled clear edge capture after %d"
" timeouts\n", dev->cw_err);
dev->cw = 0;
dev->cw_err = 0;
diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
index d9d566f70ed1..a76685c147ee 100644
--- a/drivers/pps/kapi.c
+++ b/drivers/pps/kapi.c
@@ -41,7 +41,7 @@ static void pps_add_offset(struct pps_ktime *ts, struct pps_ktime *offset)
static void pps_echo_client_default(struct pps_device *pps, int event,
void *data)
{
- dev_info(pps->dev, "echo %s %s\n",
+ dev_info(&pps->dev, "echo %s %s\n",
event & PPS_CAPTUREASSERT ? "assert" : "",
event & PPS_CAPTURECLEAR ? "clear" : "");
}
@@ -112,7 +112,7 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
goto kfree_pps;
}
- dev_info(pps->dev, "new PPS source %s\n", info->name);
+ dev_info(&pps->dev, "new PPS source %s\n", info->name);
return pps;
@@ -166,7 +166,7 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
/* check event type */
BUG_ON((event & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR)) == 0);
- dev_dbg(pps->dev, "PPS event at %lld.%09ld\n",
+ dev_dbg(&pps->dev, "PPS event at %lld.%09ld\n",
(s64)ts->ts_real.tv_sec, ts->ts_real.tv_nsec);
timespec_to_pps_ktime(&ts_real, ts->ts_real);
@@ -188,7 +188,7 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
/* Save the time stamp */
pps->assert_tu = ts_real;
pps->assert_sequence++;
- dev_dbg(pps->dev, "capture assert seq #%u\n",
+ dev_dbg(&pps->dev, "capture assert seq #%u\n",
pps->assert_sequence);
captured = ~0;
@@ -202,7 +202,7 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
/* Save the time stamp */
pps->clear_tu = ts_real;
pps->clear_sequence++;
- dev_dbg(pps->dev, "capture clear seq #%u\n",
+ dev_dbg(&pps->dev, "capture clear seq #%u\n",
pps->clear_sequence);
captured = ~0;
diff --git a/drivers/pps/kc.c b/drivers/pps/kc.c
index 50dc59af45be..fbd23295afd7 100644
--- a/drivers/pps/kc.c
+++ b/drivers/pps/kc.c
@@ -43,11 +43,11 @@ int pps_kc_bind(struct pps_device *pps, struct pps_bind_args *bind_args)
pps_kc_hardpps_mode = 0;
pps_kc_hardpps_dev = NULL;
spin_unlock_irq(&pps_kc_hardpps_lock);
- dev_info(pps->dev, "unbound kernel"
+ dev_info(&pps->dev, "unbound kernel"
" consumer\n");
} else {
spin_unlock_irq(&pps_kc_hardpps_lock);
- dev_err(pps->dev, "selected kernel consumer"
+ dev_err(&pps->dev, "selected kernel consumer"
" is not bound\n");
return -EINVAL;
}
@@ -57,11 +57,11 @@ int pps_kc_bind(struct pps_device *pps, struct pps_bind_args *bind_args)
pps_kc_hardpps_mode = bind_args->edge;
pps_kc_hardpps_dev = pps;
spin_unlock_irq(&pps_kc_hardpps_lock);
- dev_info(pps->dev, "bound kernel consumer: "
+ dev_info(&pps->dev, "bound kernel consumer: "
"edge=0x%x\n", bind_args->edge);
} else {
spin_unlock_irq(&pps_kc_hardpps_lock);
- dev_err(pps->dev, "another kernel consumer"
+ dev_err(&pps->dev, "another kernel consumer"
" is already bound\n");
return -EINVAL;
}
@@ -83,7 +83,7 @@ void pps_kc_remove(struct pps_device *pps)
pps_kc_hardpps_mode = 0;
pps_kc_hardpps_dev = NULL;
spin_unlock_irq(&pps_kc_hardpps_lock);
- dev_info(pps->dev, "unbound kernel consumer"
+ dev_info(&pps->dev, "unbound kernel consumer"
" on device removal\n");
} else
spin_unlock_irq(&pps_kc_hardpps_lock);
diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 25d47907db17..6a02245ea35f 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -25,7 +25,7 @@
* Local variables
*/
-static dev_t pps_devt;
+static int pps_major;
static struct class *pps_class;
static DEFINE_MUTEX(pps_idr_lock);
@@ -62,7 +62,7 @@ static int pps_cdev_pps_fetch(struct pps_device *pps, struct pps_fdata *fdata)
else {
unsigned long ticks;
- dev_dbg(pps->dev, "timeout %lld.%09d\n",
+ dev_dbg(&pps->dev, "timeout %lld.%09d\n",
(long long) fdata->timeout.sec,
fdata->timeout.nsec);
ticks = fdata->timeout.sec * HZ;
@@ -80,7 +80,7 @@ static int pps_cdev_pps_fetch(struct pps_device *pps, struct pps_fdata *fdata)
/* Check for pending signals */
if (err == -ERESTARTSYS) {
- dev_dbg(pps->dev, "pending signal caught\n");
+ dev_dbg(&pps->dev, "pending signal caught\n");
return -EINTR;
}
@@ -98,7 +98,7 @@ static long pps_cdev_ioctl(struct file *file,
switch (cmd) {
case PPS_GETPARAMS:
- dev_dbg(pps->dev, "PPS_GETPARAMS\n");
+ dev_dbg(&pps->dev, "PPS_GETPARAMS\n");
spin_lock_irq(&pps->lock);
@@ -114,7 +114,7 @@ static long pps_cdev_ioctl(struct file *file,
break;
case PPS_SETPARAMS:
- dev_dbg(pps->dev, "PPS_SETPARAMS\n");
+ dev_dbg(&pps->dev, "PPS_SETPARAMS\n");
/* Check the capabilities */
if (!capable(CAP_SYS_TIME))
@@ -124,14 +124,14 @@ static long pps_cdev_ioctl(struct file *file,
if (err)
return -EFAULT;
if (!(params.mode & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR))) {
- dev_dbg(pps->dev, "capture mode unspecified (%x)\n",
+ dev_dbg(&pps->dev, "capture mode unspecified (%x)\n",
params.mode);
return -EINVAL;
}
/* Check for supported capabilities */
if ((params.mode & ~pps->info.mode) != 0) {
- dev_dbg(pps->dev, "unsupported capabilities (%x)\n",
+ dev_dbg(&pps->dev, "unsupported capabilities (%x)\n",
params.mode);
return -EINVAL;
}
@@ -144,7 +144,7 @@ static long pps_cdev_ioctl(struct file *file,
/* Restore the read only parameters */
if ((params.mode & (PPS_TSFMT_TSPEC | PPS_TSFMT_NTPFP)) == 0) {
/* section 3.3 of RFC 2783 interpreted */
- dev_dbg(pps->dev, "time format unspecified (%x)\n",
+ dev_dbg(&pps->dev, "time format unspecified (%x)\n",
params.mode);
pps->params.mode |= PPS_TSFMT_TSPEC;
}
@@ -165,7 +165,7 @@ static long pps_cdev_ioctl(struct file *file,
break;
case PPS_GETCAP:
- dev_dbg(pps->dev, "PPS_GETCAP\n");
+ dev_dbg(&pps->dev, "PPS_GETCAP\n");
err = put_user(pps->info.mode, iuarg);
if (err)
@@ -176,7 +176,7 @@ static long pps_cdev_ioctl(struct file *file,
case PPS_FETCH: {
struct pps_fdata fdata;
- dev_dbg(pps->dev, "PPS_FETCH\n");
+ dev_dbg(&pps->dev, "PPS_FETCH\n");
err = copy_from_user(&fdata, uarg, sizeof(struct pps_fdata));
if (err)
@@ -206,7 +206,7 @@ static long pps_cdev_ioctl(struct file *file,
case PPS_KC_BIND: {
struct pps_bind_args bind_args;
- dev_dbg(pps->dev, "PPS_KC_BIND\n");
+ dev_dbg(&pps->dev, "PPS_KC_BIND\n");
/* Check the capabilities */
if (!capable(CAP_SYS_TIME))
@@ -218,7 +218,7 @@ static long pps_cdev_ioctl(struct file *file,
/* Check for supported capabilities */
if ((bind_args.edge & ~pps->info.mode) != 0) {
- dev_err(pps->dev, "unsupported capabilities (%x)\n",
+ dev_err(&pps->dev, "unsupported capabilities (%x)\n",
bind_args.edge);
return -EINVAL;
}
@@ -227,7 +227,7 @@ static long pps_cdev_ioctl(struct file *file,
if (bind_args.tsformat != PPS_TSFMT_TSPEC ||
(bind_args.edge & ~PPS_CAPTUREBOTH) != 0 ||
bind_args.consumer != PPS_KC_HARDPPS) {
- dev_err(pps->dev, "invalid kernel consumer bind"
+ dev_err(&pps->dev, "invalid kernel consumer bind"
" parameters (%x)\n", bind_args.edge);
return -EINVAL;
}
@@ -259,7 +259,7 @@ static long pps_cdev_compat_ioctl(struct file *file,
struct pps_fdata fdata;
int err;
- dev_dbg(pps->dev, "PPS_FETCH\n");
+ dev_dbg(&pps->dev, "PPS_FETCH\n");
err = copy_from_user(&compat, uarg, sizeof(struct pps_fdata_compat));
if (err)
@@ -296,20 +296,36 @@ static long pps_cdev_compat_ioctl(struct file *file,
#define pps_cdev_compat_ioctl NULL
#endif
+static struct pps_device *pps_idr_get(unsigned long id)
+{
+ struct pps_device *pps;
+
+ mutex_lock(&pps_idr_lock);
+ pps = idr_find(&pps_idr, id);
+ if (pps)
+ get_device(&pps->dev);
+
+ mutex_unlock(&pps_idr_lock);
+ return pps;
+}
+
static int pps_cdev_open(struct inode *inode, struct file *file)
{
- struct pps_device *pps = container_of(inode->i_cdev,
- struct pps_device, cdev);
+ struct pps_device *pps = pps_idr_get(iminor(inode));
+
+ if (!pps)
+ return -ENODEV;
+
file->private_data = pps;
- kobject_get(&pps->dev->kobj);
return 0;
}
static int pps_cdev_release(struct inode *inode, struct file *file)
{
- struct pps_device *pps = container_of(inode->i_cdev,
- struct pps_device, cdev);
- kobject_put(&pps->dev->kobj);
+ struct pps_device *pps = file->private_data;
+
+ WARN_ON(pps->id != iminor(inode));
+ put_device(&pps->dev);
return 0;
}
@@ -331,22 +347,13 @@ static void pps_device_destruct(struct device *dev)
{
struct pps_device *pps = dev_get_drvdata(dev);
- cdev_del(&pps->cdev);
-
- /* Now we can release the ID for re-use */
pr_debug("deallocating pps%d\n", pps->id);
- mutex_lock(&pps_idr_lock);
- idr_remove(&pps_idr, pps->id);
- mutex_unlock(&pps_idr_lock);
-
- kfree(dev);
kfree(pps);
}
int pps_register_cdev(struct pps_device *pps)
{
int err;
- dev_t devt;
mutex_lock(&pps_idr_lock);
/*
@@ -363,40 +370,29 @@ int pps_register_cdev(struct pps_device *pps)
goto out_unlock;
}
pps->id = err;
- mutex_unlock(&pps_idr_lock);
-
- devt = MKDEV(MAJOR(pps_devt), pps->id);
-
- cdev_init(&pps->cdev, &pps_cdev_fops);
- pps->cdev.owner = pps->info.owner;
- err = cdev_add(&pps->cdev, devt, 1);
- if (err) {
- pr_err("%s: failed to add char device %d:%d\n",
- pps->info.name, MAJOR(pps_devt), pps->id);
+ pps->dev.class = pps_class;
+ pps->dev.parent = pps->info.dev;
+ pps->dev.devt = MKDEV(pps_major, pps->id);
+ dev_set_drvdata(&pps->dev, pps);
+ dev_set_name(&pps->dev, "pps%d", pps->id);
+ err = device_register(&pps->dev);
+ if (err)
goto free_idr;
- }
- pps->dev = device_create(pps_class, pps->info.dev, devt, pps,
- "pps%d", pps->id);
- if (IS_ERR(pps->dev)) {
- err = PTR_ERR(pps->dev);
- goto del_cdev;
- }
/* Override the release function with our own */
- pps->dev->release = pps_device_destruct;
+ pps->dev.release = pps_device_destruct;
- pr_debug("source %s got cdev (%d:%d)\n", pps->info.name,
- MAJOR(pps_devt), pps->id);
+ pr_debug("source %s got cdev (%d:%d)\n", pps->info.name, pps_major,
+ pps->id);
+ get_device(&pps->dev);
+ mutex_unlock(&pps_idr_lock);
return 0;
-del_cdev:
- cdev_del(&pps->cdev);
-
free_idr:
- mutex_lock(&pps_idr_lock);
idr_remove(&pps_idr, pps->id);
+ put_device(&pps->dev);
out_unlock:
mutex_unlock(&pps_idr_lock);
return err;
@@ -406,7 +402,13 @@ void pps_unregister_cdev(struct pps_device *pps)
{
pr_debug("unregistering pps%d\n", pps->id);
pps->lookup_cookie = NULL;
- device_destroy(pps_class, pps->dev->devt);
+ device_destroy(pps_class, pps->dev.devt);
+
+ /* Now we can release the ID for re-use */
+ mutex_lock(&pps_idr_lock);
+ idr_remove(&pps_idr, pps->id);
+ put_device(&pps->dev);
+ mutex_unlock(&pps_idr_lock);
}
/*
@@ -426,6 +428,11 @@ void pps_unregister_cdev(struct pps_device *pps)
* so that it will not be used again, even if the pps device cannot
* be removed from the idr due to pending references holding the minor
* number in use.
+ *
+ * Since pps_idr holds a reference to the device, the returned
+ * pps_device is guaranteed to be valid until pps_unregister_cdev() is
+ * called on it. But after calling pps_unregister_cdev(), it may be
+ * freed at any time.
*/
struct pps_device *pps_lookup_dev(void const *cookie)
{
@@ -448,13 +455,11 @@ EXPORT_SYMBOL(pps_lookup_dev);
static void __exit pps_exit(void)
{
class_destroy(pps_class);
- unregister_chrdev_region(pps_devt, PPS_MAX_SOURCES);
+ __unregister_chrdev(pps_major, 0, PPS_MAX_SOURCES, "pps");
}
static int __init pps_init(void)
{
- int err;
-
pps_class = class_create("pps");
if (IS_ERR(pps_class)) {
pr_err("failed to allocate class\n");
@@ -462,8 +467,9 @@ static int __init pps_init(void)
}
pps_class->dev_groups = pps_groups;
- err = alloc_chrdev_region(&pps_devt, 0, PPS_MAX_SOURCES, "pps");
- if (err < 0) {
+ pps_major = __register_chrdev(0, 0, PPS_MAX_SOURCES, "pps",
+ &pps_cdev_fops);
+ if (pps_major < 0) {
pr_err("failed to allocate char device region\n");
goto remove_class;
}
@@ -476,8 +482,7 @@ static int __init pps_init(void)
remove_class:
class_destroy(pps_class);
-
- return err;
+ return pps_major;
}
subsys_initcall(pps_init);
diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
index 78c8ac4951b5..c7abce28ed29 100644
--- a/include/linux/pps_kernel.h
+++ b/include/linux/pps_kernel.h
@@ -56,8 +56,7 @@ struct pps_device {
unsigned int id; /* PPS source unique ID */
void const *lookup_cookie; /* For pps_lookup_dev() only */
- struct cdev cdev;
- struct device *dev;
+ struct device dev;
struct fasync_struct *async_queue; /* fasync method */
spinlock_t lock;
};
--
2.45.2
