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    Subject[PATCH 4.19 067/243] sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit
    Date
    From: Xin Long <lucien.xin@gmail.com>

    [ Upstream commit 02968ccf0125d39b08ecef5946300a8a873c0942 ]

    Now sctp increases sk_wmem_alloc by 1 when doing set_owner_w for the
    skb allocked in sctp_packet_transmit and decreases by 1 when freeing
    this skb.

    But when this skb goes through networking stack, some subcomponents
    might change skb->truesize and add the same amount on sk_wmem_alloc.
    However sctp doesn't know the amount to decrease by, it would cause
    a leak on sk->sk_wmem_alloc and the sock can never be freed.

    Xiumei found this issue when it hit esp_output_head() by using sctp
    over ipsec, where skb->truesize is added and so is sk->sk_wmem_alloc.

    Since sctp has used sk_wmem_queued to count for writable space since
    Commit cd305c74b0f8 ("sctp: use sk_wmem_queued to check for writable
    space"), it's ok to fix it by counting sk_wmem_alloc by skb truesize
    in sctp_packet_transmit.

    Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
    Reported-by: Xiumei Mu <xmu@redhat.com>
    Signed-off-by: Xin Long <lucien.xin@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/sctp/output.c | 21 +--------------------
    1 file changed, 1 insertion(+), 20 deletions(-)

    diff --git a/net/sctp/output.c b/net/sctp/output.c
    index 08601223b0bfa..b0e74a3e77ec5 100644
    --- a/net/sctp/output.c
    +++ b/net/sctp/output.c
    @@ -399,25 +399,6 @@ finish:
    return retval;
    }

    -static void sctp_packet_release_owner(struct sk_buff *skb)
    -{
    - sk_free(skb->sk);
    -}
    -
    -static void sctp_packet_set_owner_w(struct sk_buff *skb, struct sock *sk)
    -{
    - skb_orphan(skb);
    - skb->sk = sk;
    - skb->destructor = sctp_packet_release_owner;
    -
    - /*
    - * The data chunks have already been accounted for in sctp_sendmsg(),
    - * therefore only reserve a single byte to keep socket around until
    - * the packet has been transmitted.
    - */
    - refcount_inc(&sk->sk_wmem_alloc);
    -}
    -
    static void sctp_packet_gso_append(struct sk_buff *head, struct sk_buff *skb)
    {
    if (SCTP_OUTPUT_CB(head)->last == head)
    @@ -604,7 +585,7 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
    if (!head)
    goto out;
    skb_reserve(head, packet->overhead + MAX_HEADER);
    - sctp_packet_set_owner_w(head, sk);
    + skb_set_owner_w(head, sk);

    /* set sctp header */
    sh = skb_push(head, sizeof(struct sctphdr));
    --
    2.20.1


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