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    Subject[PATCH AUTOSEL 4.18 50/76] bpf: Fix bpf_msg_pull_data()
    Date
    From: Tushar Dave <tushar.n.dave@oracle.com>

    [ Upstream commit 9db39f4d4f94b61e4b64b077f6ddb2bdfb533a88 ]

    Helper bpf_msg_pull_data() mistakenly reuses variable 'offset' while
    linearizing multiple scatterlist elements. Variable 'offset' is used
    to find first starting scatterlist element
    i.e. msg->data = sg_virt(&sg[first_sg]) + start - offset"

    Use different variable name while linearizing multiple scatterlist
    elements so that value contained in variable 'offset' won't get
    overwritten.

    Fixes: 015632bb30da ("bpf: sk_msg program helper bpf_sk_msg_pull_data")
    Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    net/core/filter.c | 7 +++----
    1 file changed, 3 insertions(+), 4 deletions(-)

    diff --git a/net/core/filter.c b/net/core/filter.c
    index a80b57e4aaed..963ee2e88861 100644
    --- a/net/core/filter.c
    +++ b/net/core/filter.c
    @@ -2282,7 +2282,7 @@ static const struct bpf_func_proto bpf_msg_cork_bytes_proto = {
    BPF_CALL_4(bpf_msg_pull_data,
    struct sk_msg_buff *, msg, u32, start, u32, end, u64, flags)
    {
    - unsigned int len = 0, offset = 0, copy = 0;
    + unsigned int len = 0, offset = 0, copy = 0, poffset = 0;
    int bytes = end - start, bytes_sg_total;
    struct scatterlist *sg = msg->sg_data;
    int first_sg, last_sg, i, shift;
    @@ -2338,16 +2338,15 @@ BPF_CALL_4(bpf_msg_pull_data,
    if (unlikely(!page))
    return -ENOMEM;
    p = page_address(page);
    - offset = 0;

    i = first_sg;
    do {
    from = sg_virt(&sg[i]);
    len = sg[i].length;
    - to = p + offset;
    + to = p + poffset;

    memcpy(to, from, len);
    - offset += len;
    + poffset += len;
    sg[i].length = 0;
    put_page(sg_page(&sg[i]));

    --
    2.17.1
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