Re: Kmemleak: false-positive in vring_add_indirect ?

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On Fri, Oct 4, 2013 at 1:59 AM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> Thanks!  Does this work?
>
> virtio_ring: plug kmemleak false positive.
>
> unreferenced object 0xffff88003d467e20 (size 32):
>   comm "softirq", pid 0, jiffies 4295197765 (age 6.364s)
>   hex dump (first 32 bytes):
>     28 19 bf 3d 00 00 00 00 0c 00 00 00 01 00 01 00  (..=............
>     02 dc 51 3c 00 00 00 00 56 00 00 00 00 00 00 00  ..Q<....V.......
>   backtrace:
>     [<ffffffff8152db19>] kmemleak_alloc+0x59/0xc0
>     [<ffffffff81102e93>] __kmalloc+0xf3/0x180
>     [<ffffffff812db5d6>] vring_add_indirect+0x36/0x280
>     [<ffffffff812dc59f>] virtqueue_add_outbuf+0xbf/0x4e0
>     [<ffffffff813a8b30>] start_xmit+0x1a0/0x3b0
>     [<ffffffff81445861>] dev_hard_start_xmit+0x2d1/0x4d0
>     [<ffffffff81460052>] sch_direct_xmit+0xf2/0x1c0
>     [<ffffffff81445c28>] dev_queue_xmit+0x1c8/0x460
>     [<ffffffff814e3187>] ip6_finish_output2+0x1d7/0x470
>     [<ffffffff814e34b0>] ip6_finish_output+0x90/0xb0
>     [<ffffffff814e3507>] ip6_output+0x37/0xb0
>     [<ffffffff815021eb>] igmp6_send+0x2db/0x470
>     [<ffffffff81502645>] igmp6_timer_handler+0x95/0xa0
>     [<ffffffff8104b57c>] call_timer_fn+0x2c/0x90
>     [<ffffffff8104b7ba>] run_timer_softirq+0x1da/0x1f0
>     [<ffffffff81045721>] __do_softirq+0xd1/0x1b0
>
> Address gets embedded in a descriptor via virt_to_phys().  See detach_buf,
> which frees it:
>
>         if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
>                 kfree(phys_to_virt(vq->vring.desc[i].addr));
>
> Reported-by: Christoph Paasch <christoph.paasch@xxxxxxxxxxxx>
> Fix-suggested-by: Christoph Paasch <christoph.paasch@xxxxxxxxxxxx>
> Typing-done-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c

Yes, it does work.

Tested-by: Christoph Paasch <christoph.paasch@xxxxxxxxxxxx>

This patch should be sent to stable.


Thanks,
Christoph

> index 6b4a4db..6547d46 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -173,6 +173,8 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
>         head = vq->free_head;
>         vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
>         vq->vring.desc[head].addr = virt_to_phys(desc);
> +       /* kmemleak gives a false positive, as it's hidden by virt_to_phys */
> +       kmemleak_ignore(desc);
>         vq->vring.desc[head].len = i * sizeof(struct vring_desc);
>
>         /* Update free pointer */
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