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    Subject[PATCH 5.15 007/107] skmsg: Fix wrong last sg check in sk_msg_recvmsg()
    Date
    From: Liu Jian <liujian56@huawei.com>

    [ Upstream commit 583585e48d965338e73e1eb383768d16e0922d73 ]

    Fix one kernel NULL pointer dereference as below:

    [ 224.462334] Call Trace:
    [ 224.462394] __tcp_bpf_recvmsg+0xd3/0x380
    [ 224.462441] ? sock_has_perm+0x78/0xa0
    [ 224.462463] tcp_bpf_recvmsg+0x12e/0x220
    [ 224.462494] inet_recvmsg+0x5b/0xd0
    [ 224.462534] __sys_recvfrom+0xc8/0x130
    [ 224.462574] ? syscall_trace_enter+0x1df/0x2e0
    [ 224.462606] ? __do_page_fault+0x2de/0x500
    [ 224.462635] __x64_sys_recvfrom+0x24/0x30
    [ 224.462660] do_syscall_64+0x5d/0x1d0
    [ 224.462709] entry_SYSCALL_64_after_hwframe+0x65/0xca

    In commit 9974d37ea75f ("skmsg: Fix invalid last sg check in
    sk_msg_recvmsg()"), we change last sg check to sg_is_last(),
    but in sockmap redirection case (without stream_parser/stream_verdict/
    skb_verdict), we did not mark the end of the scatterlist. Check the
    sk_msg_alloc, sk_msg_page_add, and bpf_msg_push_data functions, they all
    do not mark the end of sg. They are expected to use sg.end for end
    judgment. So the judgment of '(i != msg_rx->sg.end)' is added back here.

    Fixes: 9974d37ea75f ("skmsg: Fix invalid last sg check in sk_msg_recvmsg()")
    Signed-off-by: Liu Jian <liujian56@huawei.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Acked-by: John Fastabend <john.fastabend@gmail.com>
    Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
    Link: https://lore.kernel.org/bpf/20220809094915.150391-1-liujian56@huawei.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/core/skmsg.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/net/core/skmsg.c b/net/core/skmsg.c
    index 4ddcfac344984..054073c7cbb95 100644
    --- a/net/core/skmsg.c
    +++ b/net/core/skmsg.c
    @@ -462,7 +462,7 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,

    if (copied == len)
    break;
    - } while (!sg_is_last(sge));
    + } while ((i != msg_rx->sg.end) && !sg_is_last(sge));

    if (unlikely(peek)) {
    msg_rx = sk_psock_next_msg(psock, msg_rx);
    @@ -472,7 +472,7 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,
    }

    msg_rx->sg.start = i;
    - if (!sge->length && sg_is_last(sge)) {
    + if (!sge->length && (i == msg_rx->sg.end || sg_is_last(sge))) {
    msg_rx = sk_psock_dequeue_msg(psock);
    kfree_sk_msg(msg_rx);
    }
    --
    2.35.1


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