[PATCH 4.9 02/33] net: usb: ax88179_178a: Fix out-of-bounds accesses in RX fixup

Greg Kroah-Hartman
2022-02-21T08:51:59Z

From: Jann Horn <jannh@google.com>

commit 57bc3d3ae8c14df3ceb4e17d26ddf9eeab304581 upstream.

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: e2ca90c276e1 ("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>
---
drivers/net/usb/ax88179_178a.c | 68 +++++++++++++++++++++++------------------
1 file changed, 39 insertions(+), 29 deletions(-)

--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1369,59 +1369,69 @@ static int ax88179_rx_fixup(struct usbne
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);
memcpy(&rx_hdr, skb_tail_pointer(skb), 4);
le32_to_cpus(&rx_hdr);
-
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 *