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    Subject[PATCH 5.4 075/158] can: af_can: prevent potential access of uninitialized member in can_rcv()
    Date
    From: Anant Thazhemadam <anant.thazhemadam@gmail.com>

    [ Upstream commit c8c958a58fc67f353289986850a0edf553435702 ]

    In can_rcv(), cfd->len is uninitialized when skb->len = 0, and this
    uninitialized cfd->len is accessed nonetheless by pr_warn_once().

    Fix this uninitialized variable access by checking cfd->len's validity
    condition (cfd->len > CAN_MAX_DLEN) separately after the skb->len's
    condition is checked, and appropriately modify the log messages that
    are generated as well.
    In case either of the required conditions fail, the skb is freed and
    NET_RX_DROP is returned, same as before.

    Fixes: 8cb68751c115 ("can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once")
    Reported-by: syzbot+9bcb0c9409066696d3aa@syzkaller.appspotmail.com
    Tested-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
    Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
    Link: https://lore.kernel.org/r/20201103213906.24219-2-anant.thazhemadam@gmail.com
    Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/can/af_can.c | 19 ++++++++++++++-----
    1 file changed, 14 insertions(+), 5 deletions(-)

    diff --git a/net/can/af_can.c b/net/can/af_can.c
    index 128d37a4c2e0b..09d2329719c17 100644
    --- a/net/can/af_can.c
    +++ b/net/can/af_can.c
    @@ -675,16 +675,25 @@ static int can_rcv(struct sk_buff *skb, struct net_device *dev,
    {
    struct canfd_frame *cfd = (struct canfd_frame *)skb->data;

    - if (unlikely(dev->type != ARPHRD_CAN || skb->len != CAN_MTU ||
    - cfd->len > CAN_MAX_DLEN)) {
    - pr_warn_once("PF_CAN: dropped non conform CAN skbuf: dev type %d, len %d, datalen %d\n",
    + if (unlikely(dev->type != ARPHRD_CAN || skb->len != CAN_MTU)) {
    + pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d\n",
    + dev->type, skb->len);
    + goto free_skb;
    + }
    +
    + /* This check is made separately since cfd->len would be uninitialized if skb->len = 0. */
    + if (unlikely(cfd->len > CAN_MAX_DLEN)) {
    + pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d, datalen %d\n",
    dev->type, skb->len, cfd->len);
    - kfree_skb(skb);
    - return NET_RX_DROP;
    + goto free_skb;
    }

    can_receive(skb, dev);
    return NET_RX_SUCCESS;
    +
    +free_skb:
    + kfree_skb(skb);
    + return NET_RX_DROP;
    }

    static int canfd_rcv(struct sk_buff *skb, struct net_device *dev,
    --
    2.27.0


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