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Date: Mon, 19 Apr 2021 16:29:36 -0700 (PDT)
From: Mat Martineau <mathew.j.martineau@...ux.intel.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v3] virtio-net: page_to_skb() use build_skb when
there's sufficient tailroom
On Fri, 16 Apr 2021, Xuan Zhuo wrote:
> In page_to_skb(), if we have enough tailroom to save skb_shared_info, we
> can use build_skb to create skb directly. No need to alloc for
> additional space. And it can save a 'frags slot', which is very friendly
> to GRO.
>
> Here, if the payload of the received package is too small (less than
> GOOD_COPY_LEN), we still choose to copy it directly to the space got by
> napi_alloc_skb. So we can reuse these pages.
>
> Testing Machine:
> The four queues of the network card are bound to the cpu1.
>
> Test command:
> for ((i=0;i<5;++i)); do sockperf tp --ip 192.168.122.64 -m 1000 -t 150& done
>
> The size of the udp package is 1000, so in the case of this patch, there
> will always be enough tailroom to use build_skb. The sent udp packet
> will be discarded because there is no port to receive it. The irqsoftd
> of the machine is 100%, we observe the received quantity displayed by
> sar -n DEV 1:
>
> no build_skb: 956864.00 rxpck/s
> build_skb: 1158465.00 rxpck/s
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> Suggested-by: Jason Wang <jasowang@...hat.com>
> ---
>
> v3: fix the truesize when headroom > 0
>
> v2: conflict resolution
>
> drivers/net/virtio_net.c | 69 ++++++++++++++++++++++++++++------------
> 1 file changed, 48 insertions(+), 21 deletions(-)
Xuan,
I realize this has been merged to net-next already, but I'm getting a
use-after-free with KASAN in page_to_skb() with this patch. Reverting this
change fixes the UAF. I've included the KASAN dump below, and a couple of
comments inline.
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 101659cd4b87..8cd76037c724 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -379,21 +379,17 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> struct receive_queue *rq,
> struct page *page, unsigned int offset,
> unsigned int len, unsigned int truesize,
> - bool hdr_valid, unsigned int metasize)
> + bool hdr_valid, unsigned int metasize,
> + unsigned int headroom)
> {
> struct sk_buff *skb;
> struct virtio_net_hdr_mrg_rxbuf *hdr;
> unsigned int copy, hdr_len, hdr_padded_len;
> - char *p;
> + int tailroom, shinfo_size;
> + char *p, *hdr_p;
>
> p = page_address(page) + offset;
> -
> - /* copy small packet so we can reuse these pages for small data */
> - skb = napi_alloc_skb(&rq->napi, GOOD_COPY_LEN);
> - if (unlikely(!skb))
> - return NULL;
> -
> - hdr = skb_vnet_hdr(skb);
> + hdr_p = p;
hdr_p is assigned here, pointer to an address in the provided page...
>
> hdr_len = vi->hdr_len;
> if (vi->mergeable_rx_bufs)
(snip)
> @@ -431,7 +446,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> skb_add_rx_frag(skb, 0, page, offset, len, truesize);
> else
> put_page(page);
page is potentially released here...
> - return skb;
> + goto ok;
> }
>
> /*
> @@ -458,6 +473,18 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> if (page)
> give_pages(rq, page);
>
> +ok:
> + /* hdr_valid means no XDP, so we can copy the vnet header */
> + if (hdr_valid) {
> + hdr = skb_vnet_hdr(skb);
> + memcpy(hdr, hdr_p, hdr_len);
and hdr_p is dereferenced here.
I'm seeing this KASAN UAF at boot time in a kvm VM (Fedora 33 host and
guest, if that helps):
[ 61.202483] ==================================================================
[ 61.204005] BUG: KASAN: use-after-free in page_to_skb+0x32a/0x4b0
[ 61.205387] Read of size 12 at addr ffff888105bdf800 by task NetworkManager/579
[ 61.207035]
[ 61.207408] CPU: 0 PID: 579 Comm: NetworkManager Not tainted 5.12.0-rc7+ #2
[ 61.208715] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014
[ 61.210257] Call Trace:
[ 61.210730] <IRQ>
[ 61.211209] dump_stack+0x93/0xc2
[ 61.211996] print_address_description.constprop.0+0x18/0x130
[ 61.213310] ? page_to_skb+0x32a/0x4b0
[ 61.214318] ? page_to_skb+0x32a/0x4b0
[ 61.215085] kasan_report.cold+0x7f/0x111
[ 61.215966] ? trace_hardirqs_off+0x10/0xe0
[ 61.216823] ? page_to_skb+0x32a/0x4b0
[ 61.217809] kasan_check_range+0xf9/0x1e0
[ 61.217834] memcpy+0x20/0x60
[ 61.217848] page_to_skb+0x32a/0x4b0
[ 61.217888] receive_buf+0x1434/0x2690
[ 61.217926] ? page_to_skb+0x4b0/0x4b0
[ 61.217947] ? find_held_lock+0x85/0xa0
[ 61.217964] ? lock_release+0x1d0/0x400
[ 61.217974] ? virtnet_poll+0x1d8/0x6b0
[ 61.217983] ? detach_buf_split+0x254/0x290
[ 61.218008] ? virtqueue_get_buf_ctx_split+0x145/0x1f0
[ 61.218032] virtnet_poll+0x2a8/0x6b0
[ 61.218057] ? receive_buf+0x2690/0x2690
[ 61.218067] ? lock_release+0x400/0x400
[ 61.218119] __napi_poll+0x57/0x2f0
[ 61.229624] net_rx_action+0x4dd/0x590
[ 61.230453] ? napi_threaded_poll+0x2b0/0x2b0
[ 61.231379] ? rcu_implicit_dynticks_qs+0x430/0x430
[ 61.232429] ? lock_is_held_type+0x98/0x110
[ 61.233342] __do_softirq+0xfd/0x59d
[ 61.234131] do_softirq+0x8a/0xb0
[ 61.234896] </IRQ>
[ 61.235397] ? virtnet_open+0x10a/0x2e0
[ 61.236273] __local_bh_enable_ip+0xb1/0xc0
[ 61.237199] virtnet_open+0x11b/0x2e0
[ 61.237981] __dev_open+0x1b7/0x2c0
[ 61.238689] ? dev_set_rx_mode+0x60/0x60
[ 61.239499] ? lockdep_hardirqs_on_prepare+0x12e/0x1f0
[ 61.240523] ? __local_bh_enable_ip+0x7b/0xc0
[ 61.241399] ? trace_hardirqs_on+0x1c/0x100
[ 61.242248] __dev_change_flags+0x2e6/0x370
[ 61.243098] ? dev_set_allmulti+0x10/0x10
[ 61.243908] ? lock_chain_count+0x20/0x20
[ 61.244759] dev_change_flags+0x55/0xb0
[ 61.245595] do_setlink+0xb52/0x1950
[ 61.246385] ? rtnl_getlink+0x560/0x560
[ 61.247218] ? mark_lock+0x101/0x19c0
[ 61.248003] ? lock_chain_count+0x20/0x20
[ 61.248864] ? lock_chain_count+0x20/0x20
[ 61.249728] ? lockdep_hardirqs_on_prepare+0x1f0/0x1f0
[ 61.250821] ? memset+0x20/0x40
[ 61.251474] ? __nla_validate_parse+0xac/0x12f0
[ 61.252433] ? nla_get_range_signed+0x1c0/0x1c0
[ 61.253409] ? __lock_acquire+0x85f/0x3090
[ 61.254291] __rtnl_newlink+0x85f/0xca0
[ 61.255131] ? rtnl_setlink+0x220/0x220
[ 61.255988] ? lock_is_held_type+0x98/0x110
[ 61.256911] ? find_held_lock+0x85/0xa0
[ 61.257782] ? __is_insn_slot_addr+0xa5/0x130
[ 61.257794] ? lock_downgrade+0x390/0x390
[ 61.257802] ? stack_access_ok+0x35/0x90
[ 61.257818] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 61.257840] ? __is_insn_slot_addr+0xc4/0x130
[ 61.257859] ? kernel_text_address+0xc8/0xf0
[ 61.257876] ? __kernel_text_address+0x9/0x30
[ 61.257885] ? unwind_get_return_address+0x2a/0x40
[ 61.257893] ? create_prof_cpu_mask+0x20/0x20
[ 61.257903] ? arch_stack_walk+0x99/0xf0
[ 61.258007] ? lock_release+0x1d0/0x400
[ 61.258016] ? fs_reclaim_release+0x56/0x90
[ 61.258027] ? lock_downgrade+0x390/0x390
[ 61.258036] ? find_held_lock+0x80/0xa0
[ 61.258049] ? lock_release+0x1d0/0x400
[ 61.258059] ? lock_is_held_type+0x98/0x110
[ 61.258087] rtnl_newlink+0x4b/0x70
[ 61.258099] rtnetlink_rcv_msg+0x22c/0x5e0
[ 61.258116] ? rtnetlink_put_metrics+0x2c0/0x2c0
[ 61.258131] ? lock_acquire+0x157/0x4d0
[ 61.258140] ? netlink_deliver_tap+0xa6/0x570
[ 61.258154] ? lock_release+0x400/0x400
[ 61.258172] netlink_rcv_skb+0xc4/0x1f0
[ 61.258180] ? rtnetlink_put_metrics+0x2c0/0x2c0
[ 61.258193] ? netlink_ack+0x4f0/0x4f0
[ 61.258199] ? netlink_deliver_tap+0x129/0x570
[ 61.258234] netlink_unicast+0x2d3/0x410
[ 61.258248] ? netlink_attachskb+0x400/0x400
[ 61.258257] ? _copy_from_iter_full+0xd8/0x360
[ 61.258280] netlink_sendmsg+0x394/0x670
[ 61.258299] ? netlink_unicast+0x410/0x410
[ 61.258305] ? iovec_from_user+0xa1/0x1d0
[ 61.258327] ? netlink_unicast+0x410/0x410
[ 61.258340] sock_sendmsg+0x91/0xa0
[ 61.258353] ____sys_sendmsg+0x3b7/0x400
[ 61.258366] ? kernel_sendmsg+0x30/0x30
[ 61.258376] ? __ia32_sys_recvmmsg+0x150/0x150
[ 61.258390] ? lockdep_hardirqs_on_prepare+0x1f0/0x1f0
[ 61.258398] ? stack_trace_save+0x8c/0xc0
[ 61.258408] ? stack_trace_consume_entry+0x80/0x80
[ 61.258416] ? __fput+0x1a9/0x3d0
[ 61.258435] ___sys_sendmsg+0xd3/0x130
[ 61.258446] ? sendmsg_copy_msghdr+0x110/0x110
[ 61.258458] ? find_held_lock+0x85/0xa0
[ 61.258471] ? lock_release+0x1d0/0x400
[ 61.258479] ? __fget_files+0x133/0x210
[ 61.258490] ? lock_downgrade+0x390/0x390
[ 61.258508] ? lockdep_hardirqs_on_prepare+0x1f0/0x1f0
[ 61.258529] ? __fget_files+0x152/0x210
[ 61.258547] ? __fget_light+0x66/0xf0
[ 61.258568] __sys_sendmsg+0xae/0x120
[ 61.258578] ? __sys_sendmsg_sock+0x10/0x10
[ 61.258589] ? lockdep_hardirqs_on_prepare+0x12e/0x1f0
[ 61.258598] ? call_rcu+0x414/0x670
[ 61.258616] ? mark_held_locks+0x25/0x90
[ 61.258630] ? lockdep_hardirqs_on_prepare+0x12e/0x1f0
[ 61.258639] ? syscall_enter_from_user_mode+0x1d/0x50
[ 61.258647] ? trace_hardirqs_on+0x1c/0x100
[ 61.258662] do_syscall_64+0x33/0x40
[ 61.258670] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 61.258679] RIP: 0033:0x7fb33db83ecd
[ 61.258686] Code: 28 89 54 24 1c 48 89 74 24 10 89 7c 24 08 e8 4a ee ff ff 8b 54 24 1c 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 33 44 89 c7 48 89 44 24 08 e8 9e ee ff ff 48
[ 61.258692] RSP: 002b:00007ffc85e90e30 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
[ 61.258702] RAX: ffffffffffffffda RBX: 000055f87a7aa030 RCX: 00007fb33db83ecd
[ 61.258708] RDX: 0000000000000000 RSI: 00007ffc85e90e70 RDI: 000000000000000c
[ 61.258713] RBP: 000000000000000c R08: 0000000000000000 R09: 0000000000000000
[ 61.258717] R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
[ 61.258722] R13: 00007ffc85e90fd0 R14: 00007ffc85e90fcc R15: 0000000000000000
--
Mat Martineau
Intel
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