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    Subject[PATCH 039/104] net: check net.core.somaxconn sysctl values
    Date
    3.5.7.22 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Roman Gushchin <klamm@yandex-team.ru>

    commit 5f671d6b4ec3e6d66c2a868738af2cdea09e7509 upstream.

    It's possible to assign an invalid value to the net.core.somaxconn
    sysctl variable, because there is no checks at all.

    The sk_max_ack_backlog field of the sock structure is defined as
    unsigned short. Therefore, the backlog argument in inet_listen()
    shouldn't exceed USHRT_MAX. The backlog argument in the listen() syscall
    is truncated to the somaxconn value. So, the somaxconn value shouldn't
    exceed 65535 (USHRT_MAX).
    Also, negative values of somaxconn are meaningless.

    before:
    $ sysctl -w net.core.somaxconn=256
    net.core.somaxconn = 256
    $ sysctl -w net.core.somaxconn=65536
    net.core.somaxconn = 65536
    $ sysctl -w net.core.somaxconn=-100
    net.core.somaxconn = -100

    after:
    $ sysctl -w net.core.somaxconn=256
    net.core.somaxconn = 256
    $ sysctl -w net.core.somaxconn=65536
    error: "Invalid argument" setting key "net.core.somaxconn"
    $ sysctl -w net.core.somaxconn=-100
    error: "Invalid argument" setting key "net.core.somaxconn"

    Based on a prior patch from Changli Gao.

    Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
    Reported-by: Changli Gao <xiaosuo@gmail.com>
    Suggested-by: Eric Dumazet <edumazet@google.com>
    Acked-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [ luis: backported to 3.5: adjusted context ]
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    net/core/sysctl_net_core.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
    index a7c3684..df0dafe 100644
    --- a/net/core/sysctl_net_core.c
    +++ b/net/core/sysctl_net_core.c
    @@ -20,6 +20,9 @@
    #include <net/sock.h>
    #include <net/net_ratelimit.h>

    +static int zero = 0;
    +static int ushort_max = USHRT_MAX;
    +
    #ifdef CONFIG_RPS
    static int rps_sock_flow_sysctl(ctl_table *table, int write,
    void __user *buffer, size_t *lenp, loff_t *ppos)
    @@ -198,7 +201,9 @@ static struct ctl_table netns_core_table[] = {
    .data = &init_net.core.sysctl_somaxconn,
    .maxlen = sizeof(int),
    .mode = 0644,
    - .proc_handler = proc_dointvec
    + .extra1 = &zero,
    + .extra2 = &ushort_max,
    + .proc_handler = proc_dointvec_minmax
    },
    { }
    };
    --
    1.8.3.2


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