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    SubjectRe: [PATCH AUTOSEL 4.19 21/26] Drivers: hv: vmbus: Resolve race condition in vmbus_onoffer_rescind()
    On Wed, Feb 24, 2021 at 07:54:29AM -0500, Sasha Levin wrote:
    > From: "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
    >
    > [ Upstream commit e4d221b42354b2e2ddb9187a806afb651eee2cda ]
    >
    > 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>
    > Signed-off-by: Sasha Levin <sashal@kernel.org>

    Same here.

    Andrea


    > ---
    > drivers/hv/channel_mgmt.c | 12 ++++++++++++
    > include/linux/hyperv.h | 1 +
    > 2 files changed, 13 insertions(+)
    >
    > diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
    > index 7920b0d7e35a7..1322e799938af 100644
    > --- a/drivers/hv/channel_mgmt.c
    > +++ b/drivers/hv/channel_mgmt.c
    > @@ -954,6 +954,18 @@ 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 35461d49d3aee..59525fe25abde 100644
    > --- a/include/linux/hyperv.h
    > +++ b/include/linux/hyperv.h
    > @@ -736,6 +736,7 @@ 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;
    > --
    > 2.27.0
    >

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