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    Subject[PATCH AUTOSEL for 4.15 172/189] tipc: fix skb truesize/datasize ratio control
    Date
    From: Hoang Le <hoang.h.le@dektek.com.au>

    [ Upstream commit 55b3280d1e471795c08dbbe17325720a843e104c ]

    In commit d618d09a68e4 ("tipc: enforce valid ratio between skb truesize
    and contents") we introduced a test for ensuring that the condition
    truesize/datasize <= 4 is true for a received buffer. Unfortunately this
    test has two problems.

    - Because of the integer arithmetics the test
    if (skb->truesize / buf_roundup_len(skb) > 4) will miss all
    ratios [4 < ratio < 5], which was not the intention.
    - The buffer returned by skb_copy() inherits skb->truesize of the
    original buffer, which doesn't help the situation at all.

    In this commit, we change the ratio condition and replace skb_copy()
    with a call to skb_copy_expand() to finally get this right.

    Acked-by: Jon Maloy <jon.maloy@ericsson.com>
    Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    net/tipc/msg.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/net/tipc/msg.c b/net/tipc/msg.c
    index b0d07b35909d..fb8dda66db6d 100644
    --- a/net/tipc/msg.c
    +++ b/net/tipc/msg.c
    @@ -208,8 +208,8 @@ bool tipc_msg_validate(struct sk_buff **_skb)
    int msz, hsz;

    /* Ensure that flow control ratio condition is satisfied */
    - if (unlikely(skb->truesize / buf_roundup_len(skb) > 4)) {
    - skb = skb_copy(skb, GFP_ATOMIC);
    + if (unlikely(skb->truesize / buf_roundup_len(skb) >= 4)) {
    + skb = skb_copy_expand(skb, BUF_HEADROOM, 0, GFP_ATOMIC);
    if (!skb)
    return false;
    kfree_skb(*_skb);
    --
    2.15.1
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