On Tue, 8 Aug 2023, Mikulas Patocka wrote:
On Wed, 2 Aug 2023, Mike Snitzer wrote:
[Cc'ing Mikulas so he can take a look at this too.]
Hi
I suggest this patch (but it's only compile-tested, so please run some
testsuite on it).
Mikulas
I self-nack that patch - it doesn't work if there are multiple targets
calling dm_table_set_devices_mutex in the same table. This is not an issue
for multipath, but it will be a problem if other targets use this
functionality.
Here I'm sending a better patch that doesn't need any modification to the
targets at all.
Mikulas
From: Mikulas Patocka <mpatocka at redhat.com>
Subject: [PATCH] dm: fix a race condition in retrieve_deps
There's a race condition in the multipath target when retrieve_deps races
with multipath_message calling dm_get_device and dm_put_device.
retrieve_deps walks the list of open devices without holding any lock but
multipath may add or remove devices to the list while it is running. The
end result may be memory corruption or use-after-free memory access.
Fix this bug by introducing a new rw semaphore "devices_lock". We grab
devices_lock for read in retrieve_deps and we grab it for write in
dm_get_device and dm_put_device.
Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
Cc: sta...@vger.kernel.org
---
drivers/md/dm-core.h | 1 +
drivers/md/dm-ioctl.c | 7 ++++++-
drivers/md/dm-table.c | 32 ++++++++++++++++++++++++--------
3 files changed, 31 insertions(+), 9 deletions(-)
Index: linux-2.6/drivers/md/dm-core.h
===================================================================
--- linux-2.6.orig/drivers/md/dm-core.h
+++ linux-2.6/drivers/md/dm-core.h
@@ -214,6 +214,7 @@ struct dm_table {
/* a list of devices used by this table */
struct list_head devices;
+ struct rw_semaphore devices_lock;
/* events get handed up using this callback */
void (*event_fn)(void *data);
Index: linux-2.6/drivers/md/dm-ioctl.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-ioctl.c
+++ linux-2.6/drivers/md/dm-ioctl.c
@@ -1630,6 +1630,8 @@ static void retrieve_deps(struct dm_tabl
struct dm_dev_internal *dd;
struct dm_target_deps *deps;
+ down_read(&table->devices_lock);
+
deps = get_result_buffer(param, param_size, &len);
/*
@@ -1644,7 +1646,7 @@ static void retrieve_deps(struct dm_tabl
needed = struct_size(deps, dev, count);
if (len < needed) {
param->flags |= DM_BUFFER_FULL_FLAG;
- return;
+ goto out;
}
/*
@@ -1656,6 +1658,9 @@ static void retrieve_deps(struct dm_tabl
deps->dev[count++] = huge_encode_dev(dd->dm_dev->bdev->bd_dev);
param->data_size = param->data_start + needed;
+
+out:
+ up_read(&table->devices_lock);
}
static int table_deps(struct file *filp, struct dm_ioctl *param, size_t param_size)
Index: linux-2.6/drivers/md/dm-table.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-table.c
+++ linux-2.6/drivers/md/dm-table.c
@@ -135,6 +135,7 @@ int dm_table_create(struct dm_table **re
return -ENOMEM;
INIT_LIST_HEAD(&t->devices);
+ init_rwsem(&t->devices_lock);
if (!num_targets)
num_targets = KEYS_PER_NODE;
@@ -359,16 +360,20 @@ int __ref dm_get_device(struct dm_target
if (dev == disk_devt(t->md->disk))
return -EINVAL;
+ down_write(&t->devices_lock);
+
dd = find_device(&t->devices, dev);
if (!dd) {
dd = kmalloc(sizeof(*dd), GFP_KERNEL);
- if (!dd)
- return -ENOMEM;
+ if (!dd) {
+ r = -ENOMEM;
+ goto unlock_ret_r;
+ }
r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev);
if (r) {
kfree(dd);
- return r;
+ goto unlock_ret_r;
}
refcount_set(&dd->count, 1);
@@ -378,12 +383,17 @@ int __ref dm_get_device(struct dm_target
} else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
r = upgrade_mode(dd, mode, t->md);
if (r)
- return r;
+ goto unlock_ret_r;
}
refcount_inc(&dd->count);
out:
+ up_write(&t->devices_lock);
*result = dd->dm_dev;
return 0;
+
+unlock_ret_r:
+ up_write(&t->devices_lock);
+ return r;
}
EXPORT_SYMBOL(dm_get_device);
@@ -419,9 +429,12 @@ static int dm_set_device_limits(struct d
void dm_put_device(struct dm_target *ti, struct dm_dev *d)
{
int found = 0;
- struct list_head *devices = &ti->table->devices;
+ struct dm_table *t = ti->table;
+ struct list_head *devices = &t->devices;
struct dm_dev_internal *dd;
+ down_write(&t->devices_lock);
+
list_for_each_entry(dd, devices, list) {
if (dd->dm_dev == d) {
found = 1;
@@ -430,14 +443,17 @@ void dm_put_device(struct dm_target *ti,
}
if (!found) {
DMERR("%s: device %s not in table devices list",
- dm_device_name(ti->table->md), d->name);
- return;
+ dm_device_name(t->md), d->name);
+ goto unlock_ret;
}
if (refcount_dec_and_test(&dd->count)) {
- dm_put_table_device(ti->table->md, d);
+ dm_put_table_device(t->md, d);
list_del(&dd->list);
kfree(dd);
}
+
+unlock_ret:
+ up_write(&t->devices_lock);
}
EXPORT_SYMBOL(dm_put_device);
