Re: [PATCH net 2/2] virtio_net: fix missing lock protection on control_buf access
On Tue, 28 May 2024 12:45:32 -0400, "Michael S. Tsirkin"
wrote:
> On Wed, May 29, 2024 at 12:01:45AM +0800, Heng Qi wrote:
> > On Tue, 28 May 2024 11:46:28 -0400, "Michael S. Tsirkin"
> > wrote:
> > > On Tue, May 28, 2024 at 03:52:26PM +0800, Heng Qi wrote:
> > > > Refactored the handling of control_buf to be within the cvq_lock
> > > > critical section, mitigating race conditions between reading device
> > > > responses and new command submissions.
> > > >
> > > > Fixes: 6f45ab3e0409 ("virtio_net: Add a lock for the command VQ.")
> > > > Signed-off-by: Heng Qi
> > >
> > >
> > > I don't get what does this change. status can change immediately
> > > after you drop the mutex, can it not? what exactly is the
> > > race conditions you are worried about?
> >
> > See the following case:
> >
> > 1. Command A is acknowledged and successfully executed by the device.
> > 2. After releasing the mutex (mutex_unlock), process P1 gets preempted
> > before
> >it can read vi->ctrl->status, *which should be VIRTIO_NET_OK*.
> > 3. A new command B (like the DIM command) is issued.
> > 4. Post vi->ctrl->status being set to VIRTIO_NET_ERR by
> >virtnet_send_command_reply(), process P2 gets preempted.
> > 5. Process P1 resumes, reads *vi->ctrl->status as VIRTIO_NET_ERR*, and
> > reports
> >this error back for Command A. <-- Race causes incorrect results to be
> > read.
> >
> > Thanks.
>
>
> Why is it important that P1 gets VIRTIO_NET_OK?
> After all it is no longer the state.
The driver needs to know whether the command actually executed success.
Thanks.
>
> > >
> > > > ---
> > > > drivers/net/virtio_net.c | 4 +++-
> > > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 6b0512a628e0..3d8407d9e3d2 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -2686,6 +2686,7 @@ static bool virtnet_send_command_reply(struct
> > > > virtnet_info *vi, u8 class, u8 cmd
> > > > {
> > > > struct scatterlist *sgs[5], hdr, stat;
> > > > u32 out_num = 0, tmp, in_num = 0;
> > > > + bool ret;
> > > > int err;
> > > >
> > > > /* Caller should know better */
> > > > @@ -2731,8 +2732,9 @@ static bool virtnet_send_command_reply(struct
> > > > virtnet_info *vi, u8 class, u8 cmd
> > > > }
> > > >
> > > > unlock:
> > > > + ret = vi->ctrl->status == VIRTIO_NET_OK;
> > > > mutex_unlock(&vi->cvq_lock);
> > > > - return vi->ctrl->status == VIRTIO_NET_OK;
> > > > + return ret;
> > > > }
> > > >
> > > > static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8
> > > > cmd,
> > > > --
> > > > 2.32.0.3.g01195cf9f
> > >
>
Re: [PATCH net 2/2] virtio_net: fix missing lock protection on control_buf access
On Wed, May 29, 2024 at 12:01:45AM +0800, Heng Qi wrote:
> On Tue, 28 May 2024 11:46:28 -0400, "Michael S. Tsirkin"
> wrote:
> > On Tue, May 28, 2024 at 03:52:26PM +0800, Heng Qi wrote:
> > > Refactored the handling of control_buf to be within the cvq_lock
> > > critical section, mitigating race conditions between reading device
> > > responses and new command submissions.
> > >
> > > Fixes: 6f45ab3e0409 ("virtio_net: Add a lock for the command VQ.")
> > > Signed-off-by: Heng Qi
> >
> >
> > I don't get what does this change. status can change immediately
> > after you drop the mutex, can it not? what exactly is the
> > race conditions you are worried about?
>
> See the following case:
>
> 1. Command A is acknowledged and successfully executed by the device.
> 2. After releasing the mutex (mutex_unlock), process P1 gets preempted before
>it can read vi->ctrl->status, *which should be VIRTIO_NET_OK*.
> 3. A new command B (like the DIM command) is issued.
> 4. Post vi->ctrl->status being set to VIRTIO_NET_ERR by
>virtnet_send_command_reply(), process P2 gets preempted.
> 5. Process P1 resumes, reads *vi->ctrl->status as VIRTIO_NET_ERR*, and reports
>this error back for Command A. <-- Race causes incorrect results to be
> read.
>
> Thanks.
Why is it important that P1 gets VIRTIO_NET_OK?
After all it is no longer the state.
> >
> > > ---
> > > drivers/net/virtio_net.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 6b0512a628e0..3d8407d9e3d2 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -2686,6 +2686,7 @@ static bool virtnet_send_command_reply(struct
> > > virtnet_info *vi, u8 class, u8 cmd
> > > {
> > > struct scatterlist *sgs[5], hdr, stat;
> > > u32 out_num = 0, tmp, in_num = 0;
> > > + bool ret;
> > > int err;
> > >
> > > /* Caller should know better */
> > > @@ -2731,8 +2732,9 @@ static bool virtnet_send_command_reply(struct
> > > virtnet_info *vi, u8 class, u8 cmd
> > > }
> > >
> > > unlock:
> > > + ret = vi->ctrl->status == VIRTIO_NET_OK;
> > > mutex_unlock(&vi->cvq_lock);
> > > - return vi->ctrl->status == VIRTIO_NET_OK;
> > > + return ret;
> > > }
> > >
> > > static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8
> > > cmd,
> > > --
> > > 2.32.0.3.g01195cf9f
> >
Re: [PATCH net 2/2] virtio_net: fix missing lock protection on control_buf access
On Tue, 28 May 2024 11:46:28 -0400, "Michael S. Tsirkin"
wrote:
> On Tue, May 28, 2024 at 03:52:26PM +0800, Heng Qi wrote:
> > Refactored the handling of control_buf to be within the cvq_lock
> > critical section, mitigating race conditions between reading device
> > responses and new command submissions.
> >
> > Fixes: 6f45ab3e0409 ("virtio_net: Add a lock for the command VQ.")
> > Signed-off-by: Heng Qi
>
>
> I don't get what does this change. status can change immediately
> after you drop the mutex, can it not? what exactly is the
> race conditions you are worried about?
See the following case:
1. Command A is acknowledged and successfully executed by the device.
2. After releasing the mutex (mutex_unlock), process P1 gets preempted before
it can read vi->ctrl->status, *which should be VIRTIO_NET_OK*.
3. A new command B (like the DIM command) is issued.
4. Post vi->ctrl->status being set to VIRTIO_NET_ERR by
virtnet_send_command_reply(), process P2 gets preempted.
5. Process P1 resumes, reads *vi->ctrl->status as VIRTIO_NET_ERR*, and reports
this error back for Command A. <-- Race causes incorrect results to be read.
Thanks.
>
> > ---
> > drivers/net/virtio_net.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 6b0512a628e0..3d8407d9e3d2 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -2686,6 +2686,7 @@ static bool virtnet_send_command_reply(struct
> > virtnet_info *vi, u8 class, u8 cmd
> > {
> > struct scatterlist *sgs[5], hdr, stat;
> > u32 out_num = 0, tmp, in_num = 0;
> > + bool ret;
> > int err;
> >
> > /* Caller should know better */
> > @@ -2731,8 +2732,9 @@ static bool virtnet_send_command_reply(struct
> > virtnet_info *vi, u8 class, u8 cmd
> > }
> >
> > unlock:
> > + ret = vi->ctrl->status == VIRTIO_NET_OK;
> > mutex_unlock(&vi->cvq_lock);
> > - return vi->ctrl->status == VIRTIO_NET_OK;
> > + return ret;
> > }
> >
> > static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > --
> > 2.32.0.3.g01195cf9f
>
Re: [PATCH net 2/2] virtio_net: fix missing lock protection on control_buf access
On Tue, May 28, 2024 at 03:52:26PM +0800, Heng Qi wrote:
> Refactored the handling of control_buf to be within the cvq_lock
> critical section, mitigating race conditions between reading device
> responses and new command submissions.
>
> Fixes: 6f45ab3e0409 ("virtio_net: Add a lock for the command VQ.")
> Signed-off-by: Heng Qi
I don't get what does this change. status can change immediately
after you drop the mutex, can it not? what exactly is the
race conditions you are worried about?
> ---
> drivers/net/virtio_net.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6b0512a628e0..3d8407d9e3d2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2686,6 +2686,7 @@ static bool virtnet_send_command_reply(struct
> virtnet_info *vi, u8 class, u8 cmd
> {
> struct scatterlist *sgs[5], hdr, stat;
> u32 out_num = 0, tmp, in_num = 0;
> + bool ret;
> int err;
>
> /* Caller should know better */
> @@ -2731,8 +2732,9 @@ static bool virtnet_send_command_reply(struct
> virtnet_info *vi, u8 class, u8 cmd
> }
>
> unlock:
> + ret = vi->ctrl->status == VIRTIO_NET_OK;
> mutex_unlock(&vi->cvq_lock);
> - return vi->ctrl->status == VIRTIO_NET_OK;
> + return ret;
> }
>
> static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> --
> 2.32.0.3.g01195cf9f
