Re: [PATCH AUTOSEL 4.19 21/26] Drivers: hv: vmbus: Resolve race condition in vmbus_onoffer_rescind()
From: Andrea Parri
Date: Wed Feb 24 2021 - 09:41:57 EST
On Wed, Feb 24, 2021 at 07:54:29AM -0500, Sasha Levin wrote:
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From: "Andrea Parri (Microsoft)" <parri.andrea@xxxxxxxxx>
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[ Upstream commit e4d221b42354b2e2ddb9187a806afb651eee2cda ]
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An erroneous or malicious host could send multiple rescind messages for
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a same channel. In vmbus_onoffer_rescind(), the guest maps the channel
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ID to obtain a pointer to the channel object and it eventually releases
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such object and associated data. The host could time rescind messages
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and lead to an use-after-free. Add a new flag to the channel structure
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to make sure that only one instance of vmbus_onoffer_rescind() can get
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the reference to the channel object.
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Reported-by: Juan Vazquez <juvazq@xxxxxxxxxxxxx>
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Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
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Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
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Link: https://lore.kernel.org/r/20201209070827.29335-6-parri.andrea@xxxxxxxxx
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Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
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Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
Same here.
Andrea
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---
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drivers/hv/channel_mgmt.c | 12 ++++++++++++
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include/linux/hyperv.h | 1 +
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2 files changed, 13 insertions(+)
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diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
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index 7920b0d7e35a7..1322e799938af 100644
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--- a/drivers/hv/channel_mgmt.c
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+++ b/drivers/hv/channel_mgmt.c
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@@ -954,6 +954,18 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
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mutex_lock(&vmbus_connection.channel_mutex);
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channel = relid2channel(rescind->child_relid);
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+ if (channel != NULL) {
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+ /*
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+ * Guarantee that no other instance of vmbus_onoffer_rescind()
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+ * has got a reference to the channel object. Synchronize on
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+ * &vmbus_connection.channel_mutex.
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+ */
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+ if (channel->rescind_ref) {
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+ mutex_unlock(&vmbus_connection.channel_mutex);
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+ return;
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+ }
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+ channel->rescind_ref = true;
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+ }
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mutex_unlock(&vmbus_connection.channel_mutex);
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if (channel == NULL) {
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diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
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index 35461d49d3aee..59525fe25abde 100644
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--- a/include/linux/hyperv.h
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+++ b/include/linux/hyperv.h
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@@ -736,6 +736,7 @@ struct vmbus_channel {
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u8 monitor_bit;
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bool rescind; /* got rescind msg */
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+ bool rescind_ref; /* got rescind msg, got channel reference */
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struct completion rescind_event;
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u32 ringbuffer_gpadlhandle;
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--
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2.27.0
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