Drivers: hv: vmbus: Resolve race condition in vmbus_onoffer_rescind()

An erroneous or malicious host could send multiple rescind messages for
a same channel.  In vmbus_onoffer_rescind(), the guest maps the channel
ID to obtain a pointer to the channel object and it eventually releases
such object and associated data.  The host could time rescind messages
and lead to an use-after-free.  Add a new flag to the channel structure
to make sure that only one instance of vmbus_onoffer_rescind() can get
the reference to the channel object.

Reported-by: Juan Vazquez <juvazq@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20201209070827.29335-6-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 4072fd1f22146e6e4759ff6318685b2ee167c335..68950a1e4b63863362e4f538c18c8521d078a4ad 100644 (file)
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -1063,6 +1063,18 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 
        mutex_lock(&vmbus_connection.channel_mutex);
        channel = relid2channel(rescind->child_relid);
+       if (channel != NULL) {
+               /*
+                * Guarantee that no other instance of vmbus_onoffer_rescind()
+                * has got a reference to the channel object.  Synchronize on
+                * &vmbus_connection.channel_mutex.
+                */
+               if (channel->rescind_ref) {
+                       mutex_unlock(&vmbus_connection.channel_mutex);
+                       return;
+               }
+               channel->rescind_ref = true;
+       }
        mutex_unlock(&vmbus_connection.channel_mutex);
 
        if (channel == NULL) {

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 2ea967bc17adfc38c0e0cc2cb976e3815d6224d2..f0d48a368f131a8beea2f48da2236dd51809e373 100644 (file)
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -809,6 +809,7 @@ struct vmbus_channel {
        u8 monitor_bit;
 
        bool rescind; /* got rescind msg */
+       bool rescind_ref; /* got rescind msg, got channel reference */
        struct completion rescind_event;
 
        u32 ringbuffer_gpadlhandle;