Commit a0ccc147 authored Jan 16, 2020 by Andrey Shvetsov Committed by Greg Kroah-Hartman Jan 29, 2020

UPSTREAM: staging: most: net: fix buffer overflow



If the length of the socket buffer is 0xFFFFFFFF (max size for an
unsigned int), then payload_len becomes 0xFFFFFFF1 after subtracting 14
(ETH_HLEN).  Then, mdp_len is set to payload_len + 16 (MDP_HDR_LEN)
which overflows and results in a value of 2.  These values for
payload_len and mdp_len will pass current buffer size checks.

This patch checks if derived from skb->len sum may overflow.

The check is based on the following idea:

For any `unsigned V1, V2` and derived `unsigned SUM = V1 + V2`,
`V1 + V2` overflows iif `SUM < V1`.

Bug: 143560807
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200116172238.6046-1-andrey.shvetsov@microchip.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 4d1356ac12f4d5180d0df345d85ff0ee42b89c72)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I71197b2963735ba181314332737fc0c1ca2cab96

parent ea4eb1a8

drivers/staging/most/aim-network/networking.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -87,6 +87,11 @@ static int skb_to_mamac(const struct sk_buff skb, struct mbo mbo)
		unsigned int payload_len = skb->len - ETH_HLEN;
		unsigned int mdp_len = payload_len + MDP_HDR_LEN;

		if (mdp_len < skb->len) {
		pr_err("drop: too large packet! (%u)\n", skb->len);
		return -EINVAL;
		}

		if (mbo->buffer_length < mdp_len) {
		pr_err("drop: too small buffer! (%d for %d)\n",
		mbo->buffer_length, mdp_len);
		@@ -134,6 +139,11 @@ static int skb_to_mep(const struct sk_buff skb, struct mbo mbo)
		u8 *buff = mbo->virt_address;
		unsigned int mep_len = skb->len + MEP_HDR_LEN;

		if (mep_len < skb->len) {
		pr_err("drop: too large packet! (%u)\n", skb->len);
		return -EINVAL;
		}

		if (mbo->buffer_length < mep_len) {
		pr_err("drop: too small buffer! (%d for %d)\n",
		mbo->buffer_length, mep_len);