net: usb: ax88179_178a: Fix out-of-bounds accesses in RX fixup

ax88179_rx_fixup() contains several out-of-bounds accesses that can be
triggered by a malicious (or defective) USB device, in particular:

 - The metadata array (hdr_off..hdr_off+2*pkt_cnt) can be out of bounds,
   causing OOB reads and (on big-endian systems) OOB endianness flips.
 - A packet can overlap the metadata array, causing a later OOB
   endianness flip to corrupt data used by a cloned SKB that has already
   been handed off into the network stack.
 - A packet SKB can be constructed whose tail is far beyond its end,
   causing out-of-bounds heap data to be considered part of the SKB's
   data.

I have tested that this can be used by a malicious USB device to send a
bogus ICMPv6 Echo Request and receive an ICMPv6 Echo Reply in response
that contains random kernel heap data.
It's probably also possible to get OOB writes from this on a
little-endian system somehow - maybe by triggering skb_cow() via IP
options processing -, but I haven't tested that.

Fixes: ce13f848757a ("ax88179_178a: ASIX AX88179_178A USB 3.0/2.0 to gigabit ethernet adapter driver")
Cc: stable@kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/usb/ax88179_178a.c b/drivers/net/usb/ax88179_178a.c
index 1a627ba4b850212c32bd7b7c1703dcd4a0472059..a31098981a652eb8f06c05f604e233e46b1f52c5 100644 (file)
--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1468,58 +1468,68 @@ static int ax88179_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
        u16 hdr_off;
        u32 *pkt_hdr;
 
-       /* This check is no longer done by usbnet */
-       if (skb->len < dev->net->hard_header_len)
+       /* At the end of the SKB, there's a header telling us how many packets
+        * are bundled into this buffer and where we can find an array of
+        * per-packet metadata (which contains elements encoded into u16).
+        */
+       if (skb->len < 4)
                return 0;
-
        skb_trim(skb, skb->len - 4);
        rx_hdr = get_unaligned_le32(skb_tail_pointer(skb));
-
        pkt_cnt = (u16)rx_hdr;
        hdr_off = (u16)(rx_hdr >> 16);
+
+       if (pkt_cnt == 0)
+               return 0;
+
+       /* Make sure that the bounds of the metadata array are inside the SKB
+        * (and in front of the counter at the end).
+        */
+       if (pkt_cnt * 2 + hdr_off > skb->len)
+               return 0;
        pkt_hdr = (u32 *)(skb->data + hdr_off);
 
-       while (pkt_cnt--) {
+       /* Packets must not overlap the metadata array */
+       skb_trim(skb, hdr_off);
+
+       for (; ; pkt_cnt--, pkt_hdr++) {
                u16 pkt_len;
 
                le32_to_cpus(pkt_hdr);
                pkt_len = (*pkt_hdr >> 16) & 0x1fff;
 
-               /* Check CRC or runt packet */
-               if ((*pkt_hdr & AX_RXHDR_CRC_ERR) ||
-                   (*pkt_hdr & AX_RXHDR_DROP_ERR)) {
-                       skb_pull(skb, (pkt_len + 7) & 0xFFF8);
-                       pkt_hdr++;
-                       continue;
-               }
-
-               if (pkt_cnt == 0) {
-                       skb->len = pkt_len;
-                       /* Skip IP alignment pseudo header */
-                       skb_pull(skb, 2);
-                       skb_set_tail_pointer(skb, skb->len);
-                       skb->truesize = pkt_len + sizeof(struct sk_buff);
-                       ax88179_rx_checksum(skb, pkt_hdr);
-                       return 1;
-               }
+               if (pkt_len > skb->len)
+                       return 0;
 
-               ax_skb = skb_clone(skb, GFP_ATOMIC);
-               if (ax_skb) {
+               /* Check CRC or runt packet */
+               if (((*pkt_hdr & (AX_RXHDR_CRC_ERR | AX_RXHDR_DROP_ERR)) == 0) &&
+                   pkt_len >= 2 + ETH_HLEN) {
+                       bool last = (pkt_cnt == 0);
+
+                       if (last) {
+                               ax_skb = skb;
+                       } else {
+                               ax_skb = skb_clone(skb, GFP_ATOMIC);
+                               if (!ax_skb)
+                                       return 0;
+                       }
                        ax_skb->len = pkt_len;
                        /* Skip IP alignment pseudo header */
                        skb_pull(ax_skb, 2);
                        skb_set_tail_pointer(ax_skb, ax_skb->len);
                        ax_skb->truesize = pkt_len + sizeof(struct sk_buff);
                        ax88179_rx_checksum(ax_skb, pkt_hdr);
+
+                       if (last)
+                               return 1;
+
                        usbnet_skb_return(dev, ax_skb);
-               } else {
-                       return 0;
                }
 
-               skb_pull(skb, (pkt_len + 7) & 0xFFF8);
-               pkt_hdr++;
+               /* Trim this packet away from the SKB */
+               if (!skb_pull(skb, (pkt_len + 7) & 0xFFF8))
+                       return 0;
        }
-       return 1;
 }
 
 static struct sk_buff *