virtio-net: fix use-after-free in skb_gro_receive

When "headroom" > 0, the actual allocated memory space is the entire
page, so the address of the page should be used when passing it to
build_skb().

BUG: KASAN: use-after-free in skb_gro_receive (net/core/skbuff.c:4260)
Write of size 16 at addr ffff88811619fffc by task kworker/u9:0/534
CPU: 2 PID: 534 Comm: kworker/u9:0 Not tainted 5.12.0-rc7-custom-16372-gb150be05b806 #3382
Hardware name: QEMU MSN2700, BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
Workqueue: xprtiod xs_stream_data_receive_workfn [sunrpc]
Call Trace:
 <IRQ>
dump_stack (lib/dump_stack.c:122)
print_address_description.constprop.0 (mm/kasan/report.c:233)
kasan_report.cold (mm/kasan/report.c:400 mm/kasan/report.c:416)
skb_gro_receive (net/core/skbuff.c:4260)
tcp_gro_receive (net/ipv4/tcp_offload.c:266 (discriminator 1))
tcp4_gro_receive (net/ipv4/tcp_offload.c:316)
inet_gro_receive (net/ipv4/af_inet.c:1545 (discriminator 2))
dev_gro_receive (net/core/dev.c:6075)
napi_gro_receive (net/core/dev.c:6168 net/core/dev.c:6198)
receive_buf (drivers/net/virtio_net.c:1151) virtio_net
virtnet_poll (drivers/net/virtio_net.c:1415 drivers/net/virtio_net.c:1519) virtio_net
__napi_poll (net/core/dev.c:6964)
net_rx_action (net/core/dev.c:7033 net/core/dev.c:7118)
__do_softirq (./arch/x86/include/asm/jump_label.h:25 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:346)
irq_exit_rcu (kernel/softirq.c:221 kernel/softirq.c:422 kernel/softirq.c:434)
common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 14))
</IRQ>

Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Reported-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 74d2d49264f3f3b7039be70331d4a44c53b8cc28..7fda2ae4c40f0c228bdb5048074676fcc03462f7 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -387,7 +387,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
        unsigned int copy, hdr_len, hdr_padded_len;
        struct page *page_to_free = NULL;
        int tailroom, shinfo_size;
-       char *p, *hdr_p;
+       char *p, *hdr_p, *buf;
 
        p = page_address(page) + offset;
        hdr_p = p;
@@ -403,11 +403,15 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
         * space are aligned.
         */
        if (headroom) {
-               /* The actual allocated space size is PAGE_SIZE. */
+               /* Buffers with headroom use PAGE_SIZE as alloc size,
+                * see add_recvbuf_mergeable() + get_mergeable_buf_len()
+                */
                truesize = PAGE_SIZE;
                tailroom = truesize - len - offset;
+               buf = page_address(page);
        } else {
                tailroom = truesize - len;
+               buf = p;
        }
 
        len -= hdr_len;
@@ -416,11 +420,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 
        shinfo_size = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
+       /* copy small packet so we can reuse these pages */
        if (!NET_IP_ALIGN && len > GOOD_COPY_LEN && tailroom >= shinfo_size) {
-               skb = build_skb(p, truesize);
+               skb = build_skb(buf, truesize);
                if (unlikely(!skb))
                        return NULL;
 
+               skb_reserve(skb, p - buf);
                skb_put(skb, len);
                goto ok;
        }