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Subject[PATCH v3 3/3] Drivers: hv: vmbus: Fix race condition with new ring_buffer_info mutex
Fix a race condition that can result in a ring buffer pointer being set
to null while a "_show" function is reading the ring buffer's data. This
problem was discussed here: https://lkml.org/lkml/2018/10/18/779

To fix the race condition, add a new mutex lock to the
"hv_ring_buffer_info" struct. Add a new function,
"hv_ringbuffer_pre_init()", where a channel's inbound and outbound
ring_buffer_info mutex locks are initialized.

Acquire/release the locks in the "hv_ringbuffer_cleanup()" function,
which is where the ring buffer pointers are set to null.

Acquire/release the locks in the four channel-level "_show" functions
that access ring buffer data. Remove the "const" qualifier from the
"vmbus_channel" parameter and the "rbi" variable of the channel-level
"_show" functions so that the locks can be acquired/released in these
functions.

Acquire/release the locks in hv_ringbuffer_get_debuginfo(). Remove the
"const" qualifier from the "hv_ring_buffer_info" parameter so that the
locks can be acquired/released in this function.

Signed-off-by: Kimberly Brown <kimbrownkd@gmail.com>
---
drivers/hv/channel_mgmt.c | 2 +
drivers/hv/hyperv_vmbus.h | 1 +
drivers/hv/ring_buffer.c | 19 ++++++++-
drivers/hv/vmbus_drv.c | 82 +++++++++++++++++++++++++--------------
include/linux/hyperv.h | 7 +++-
5 files changed, 79 insertions(+), 32 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 9d7f9c1c60c7..14543059cc3e 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -336,6 +336,8 @@ static struct vmbus_channel *alloc_channel(void)
tasklet_init(&channel->callback_event,
vmbus_on_event, (unsigned long)channel);

+ hv_ringbuffer_pre_init(channel);
+
return channel;
}

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index a94aab94e0b5..e5467b821f41 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -193,6 +193,7 @@ extern void hv_synic_clockevents_cleanup(void);

/* Interface */

+void hv_ringbuffer_pre_init(struct vmbus_channel *channel);

int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
struct page *pages, u32 pagecnt);
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 0386ff48c5ea..121a01c43298 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -166,14 +166,18 @@ hv_get_ringbuffer_availbytes(const struct hv_ring_buffer_info *rbi,
}

/* Get various debug metrics for the specified ring buffer. */
-int hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
+int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
struct hv_ring_buffer_debug_info *debug_info)
{
u32 bytes_avail_towrite;
u32 bytes_avail_toread;

- if (!ring_info->ring_buffer)
+ mutex_lock(&ring_info->ring_buffer_mutex);
+
+ if (!ring_info->ring_buffer) {
+ mutex_unlock(&ring_info->ring_buffer_mutex);
return -EINVAL;
+ }

hv_get_ringbuffer_availbytes(ring_info,
&bytes_avail_toread,
@@ -184,10 +188,19 @@ int hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
debug_info->current_write_index = ring_info->ring_buffer->write_index;
debug_info->current_interrupt_mask
= ring_info->ring_buffer->interrupt_mask;
+ mutex_unlock(&ring_info->ring_buffer_mutex);
+
return 0;
}
EXPORT_SYMBOL_GPL(hv_ringbuffer_get_debuginfo);

+/* Initialize a channel's ring buffer info mutex locks */
+void hv_ringbuffer_pre_init(struct vmbus_channel *channel)
+{
+ mutex_init(&channel->inbound.ring_buffer_mutex);
+ mutex_init(&channel->outbound.ring_buffer_mutex);
+}
+
/* Initialize the ring buffer. */
int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
struct page *pages, u32 page_cnt)
@@ -240,8 +253,10 @@ int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
/* Cleanup the ring buffer. */
void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
{
+ mutex_lock(&ring_info->ring_buffer_mutex);
vunmap(ring_info->ring_buffer);
ring_info->ring_buffer = NULL;
+ mutex_unlock(&ring_info->ring_buffer_mutex);
}

/* Write to the ring buffer. */
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 7f15c41d952e..84f3a510b4c9 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1410,7 +1410,7 @@ static void vmbus_chan_release(struct kobject *kobj)

struct vmbus_chan_attribute {
struct attribute attr;
- ssize_t (*show)(const struct vmbus_channel *chan, char *buf);
+ ssize_t (*show)(struct vmbus_channel *chan, char *buf);
ssize_t (*store)(struct vmbus_channel *chan,
const char *buf, size_t count);
};
@@ -1429,7 +1429,7 @@ static ssize_t vmbus_chan_attr_show(struct kobject *kobj,
{
const struct vmbus_chan_attribute *attribute
= container_of(attr, struct vmbus_chan_attribute, attr);
- const struct vmbus_channel *chan
+ struct vmbus_channel *chan
= container_of(kobj, struct vmbus_channel, kobj);

if (!attribute->show)
@@ -1442,57 +1442,81 @@ static const struct sysfs_ops vmbus_chan_sysfs_ops = {
.show = vmbus_chan_attr_show,
};

-static ssize_t out_mask_show(const struct vmbus_channel *channel, char *buf)
+static ssize_t out_mask_show(struct vmbus_channel *channel, char *buf)
{
- const struct hv_ring_buffer_info *rbi = &channel->outbound;
+ struct hv_ring_buffer_info *rbi = &channel->outbound;
+ ssize_t ret;

- if (!rbi->ring_buffer)
+ mutex_lock(&rbi->ring_buffer_mutex);
+ if (!rbi->ring_buffer) {
+ mutex_unlock(&rbi->ring_buffer_mutex);
return -EINVAL;
+ }

- return sprintf(buf, "%u\n", rbi->ring_buffer->interrupt_mask);
+ ret = sprintf(buf, "%u\n", rbi->ring_buffer->interrupt_mask);
+ mutex_unlock(&rbi->ring_buffer_mutex);
+ return ret;
}
static VMBUS_CHAN_ATTR_RO(out_mask);

-static ssize_t in_mask_show(const struct vmbus_channel *channel, char *buf)
+static ssize_t in_mask_show(struct vmbus_channel *channel, char *buf)
{
- const struct hv_ring_buffer_info *rbi = &channel->inbound;
+ struct hv_ring_buffer_info *rbi = &channel->inbound;
+ ssize_t ret;

- if (!rbi->ring_buffer)
+ mutex_lock(&rbi->ring_buffer_mutex);
+ if (!rbi->ring_buffer) {
+ mutex_unlock(&rbi->ring_buffer_mutex);
return -EINVAL;
+ }

- return sprintf(buf, "%u\n", rbi->ring_buffer->interrupt_mask);
+ ret = sprintf(buf, "%u\n", rbi->ring_buffer->interrupt_mask);
+ mutex_unlock(&rbi->ring_buffer_mutex);
+ return ret;
}
static VMBUS_CHAN_ATTR_RO(in_mask);

-static ssize_t read_avail_show(const struct vmbus_channel *channel, char *buf)
+static ssize_t read_avail_show(struct vmbus_channel *channel, char *buf)
{
- const struct hv_ring_buffer_info *rbi = &channel->inbound;
+ struct hv_ring_buffer_info *rbi = &channel->inbound;
+ ssize_t ret;

- if (!rbi->ring_buffer)
+ mutex_lock(&rbi->ring_buffer_mutex);
+ if (!rbi->ring_buffer) {
+ mutex_unlock(&rbi->ring_buffer_mutex);
return -EINVAL;
+ }

- return sprintf(buf, "%u\n", hv_get_bytes_to_read(rbi));
+ ret = sprintf(buf, "%u\n", hv_get_bytes_to_read(rbi));
+ mutex_unlock(&rbi->ring_buffer_mutex);
+ return ret;
}
static VMBUS_CHAN_ATTR_RO(read_avail);

-static ssize_t write_avail_show(const struct vmbus_channel *channel, char *buf)
+static ssize_t write_avail_show(struct vmbus_channel *channel, char *buf)
{
- const struct hv_ring_buffer_info *rbi = &channel->outbound;
+ struct hv_ring_buffer_info *rbi = &channel->outbound;
+ ssize_t ret;

- if (!rbi->ring_buffer)
+ mutex_lock(&rbi->ring_buffer_mutex);
+ if (!rbi->ring_buffer) {
+ mutex_unlock(&rbi->ring_buffer_mutex);
return -EINVAL;
+ }

- return sprintf(buf, "%u\n", hv_get_bytes_to_write(rbi));
+ ret = sprintf(buf, "%u\n", hv_get_bytes_to_write(rbi));
+ mutex_unlock(&rbi->ring_buffer_mutex);
+ return ret;
}
static VMBUS_CHAN_ATTR_RO(write_avail);

-static ssize_t show_target_cpu(const struct vmbus_channel *channel, char *buf)
+static ssize_t show_target_cpu(struct vmbus_channel *channel, char *buf)
{
return sprintf(buf, "%u\n", channel->target_cpu);
}
static VMBUS_CHAN_ATTR(cpu, S_IRUGO, show_target_cpu, NULL);

-static ssize_t channel_pending_show(const struct vmbus_channel *channel,
+static ssize_t channel_pending_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%d\n",
@@ -1501,7 +1525,7 @@ static ssize_t channel_pending_show(const struct vmbus_channel *channel,
}
static VMBUS_CHAN_ATTR(pending, S_IRUGO, channel_pending_show, NULL);

-static ssize_t channel_latency_show(const struct vmbus_channel *channel,
+static ssize_t channel_latency_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%d\n",
@@ -1510,19 +1534,19 @@ static ssize_t channel_latency_show(const struct vmbus_channel *channel,
}
static VMBUS_CHAN_ATTR(latency, S_IRUGO, channel_latency_show, NULL);

-static ssize_t channel_interrupts_show(const struct vmbus_channel *channel, char *buf)
+static ssize_t channel_interrupts_show(struct vmbus_channel *channel, char *buf)
{
return sprintf(buf, "%llu\n", channel->interrupts);
}
static VMBUS_CHAN_ATTR(interrupts, S_IRUGO, channel_interrupts_show, NULL);

-static ssize_t channel_events_show(const struct vmbus_channel *channel, char *buf)
+static ssize_t channel_events_show(struct vmbus_channel *channel, char *buf)
{
return sprintf(buf, "%llu\n", channel->sig_events);
}
static VMBUS_CHAN_ATTR(events, S_IRUGO, channel_events_show, NULL);

-static ssize_t channel_intr_in_full_show(const struct vmbus_channel *channel,
+static ssize_t channel_intr_in_full_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%llu\n",
@@ -1530,7 +1554,7 @@ static ssize_t channel_intr_in_full_show(const struct vmbus_channel *channel,
}
static VMBUS_CHAN_ATTR(intr_in_full, 0444, channel_intr_in_full_show, NULL);

-static ssize_t channel_intr_out_empty_show(const struct vmbus_channel *channel,
+static ssize_t channel_intr_out_empty_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%llu\n",
@@ -1538,7 +1562,7 @@ static ssize_t channel_intr_out_empty_show(const struct vmbus_channel *channel,
}
static VMBUS_CHAN_ATTR(intr_out_empty, 0444, channel_intr_out_empty_show, NULL);

-static ssize_t channel_out_full_first_show(const struct vmbus_channel *channel,
+static ssize_t channel_out_full_first_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%llu\n",
@@ -1546,7 +1570,7 @@ static ssize_t channel_out_full_first_show(const struct vmbus_channel *channel,
}
static VMBUS_CHAN_ATTR(out_full_first, 0444, channel_out_full_first_show, NULL);

-static ssize_t channel_out_full_total_show(const struct vmbus_channel *channel,
+static ssize_t channel_out_full_total_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%llu\n",
@@ -1554,14 +1578,14 @@ static ssize_t channel_out_full_total_show(const struct vmbus_channel *channel,
}
static VMBUS_CHAN_ATTR(out_full_total, 0444, channel_out_full_total_show, NULL);

-static ssize_t subchannel_monitor_id_show(const struct vmbus_channel *channel,
+static ssize_t subchannel_monitor_id_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%u\n", channel->offermsg.monitorid);
}
static VMBUS_CHAN_ATTR(monitor_id, S_IRUGO, subchannel_monitor_id_show, NULL);

-static ssize_t subchannel_id_show(const struct vmbus_channel *channel,
+static ssize_t subchannel_id_show(struct vmbus_channel *channel,
char *buf)
{
return sprintf(buf, "%u\n",
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 64698ec8f2ac..8b9a93c99c9b 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -141,6 +141,11 @@ struct hv_ring_buffer_info {

u32 ring_datasize; /* < ring_size */
u32 priv_read_index;
+ /*
+ * The ring buffer mutex lock. This lock prevents the ring buffer from
+ * being freed while the ring buffer is being accessed.
+ */
+ struct mutex ring_buffer_mutex;
};


@@ -1206,7 +1211,7 @@ struct hv_ring_buffer_debug_info {
};


-int hv_ringbuffer_get_debuginfo(const struct hv_ring_buffer_info *ring_info,
+int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
struct hv_ring_buffer_debug_info *debug_info);

/* Vmbus interface */
--
2.17.1
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