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    Subject[ 32/49] cipso: dont follow a NULL pointer when setsockopt() is called
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    From: Greg KH <gregkh@linuxfoundation.org>

    3.0-stable review patch. If anyone has any objections, please let me know.

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


    From: Paul Moore <pmoore@redhat.com>

    [ Upstream commit 89d7ae34cdda4195809a5a987f697a517a2a3177 ]

    As reported by Alan Cox, and verified by Lin Ming, when a user
    attempts to add a CIPSO option to a socket using the CIPSO_V4_TAG_LOCAL
    tag the kernel dies a terrible death when it attempts to follow a NULL
    pointer (the skb argument to cipso_v4_validate() is NULL when called via
    the setsockopt() syscall).

    This patch fixes this by first checking to ensure that the skb is
    non-NULL before using it to find the incoming network interface. In
    the unlikely case where the skb is NULL and the user attempts to add
    a CIPSO option with the _TAG_LOCAL tag we return an error as this is
    not something we want to allow.

    A simple reproducer, kindly supplied by Lin Ming, although you must
    have the CIPSO DOI #3 configure on the system first or you will be
    caught early in cipso_v4_validate():

    #include <sys/types.h>
    #include <sys/socket.h>
    #include <linux/ip.h>
    #include <linux/in.h>
    #include <string.h>

    struct local_tag {
    char type;
    char length;
    char info[4];
    };

    struct cipso {
    char type;
    char length;
    char doi[4];
    struct local_tag local;
    };

    int main(int argc, char **argv)
    {
    int sockfd;
    struct cipso cipso = {
    .type = IPOPT_CIPSO,
    .length = sizeof(struct cipso),
    .local = {
    .type = 128,
    .length = sizeof(struct local_tag),
    },
    };

    memset(cipso.doi, 0, 4);
    cipso.doi[3] = 3;

    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    #define SOL_IP 0
    setsockopt(sockfd, SOL_IP, IP_OPTIONS,
    &cipso, sizeof(struct cipso));

    return 0;
    }

    CC: Lin Ming <mlin@ss.pku.edu.cn>
    Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Signed-off-by: Paul Moore <pmoore@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/cipso_ipv4.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    --- a/net/ipv4/cipso_ipv4.c
    +++ b/net/ipv4/cipso_ipv4.c
    @@ -1725,8 +1725,10 @@ int cipso_v4_validate(const struct sk_bu
    case CIPSO_V4_TAG_LOCAL:
    /* This is a non-standard tag that we only allow for
    * local connections, so if the incoming interface is
    - * not the loopback device drop the packet. */
    - if (!(skb->dev->flags & IFF_LOOPBACK)) {
    + * not the loopback device drop the packet. Further,
    + * there is no legitimate reason for setting this from
    + * userspace so reject it if skb is NULL. */
    + if (skb == NULL || !(skb->dev->flags & IFF_LOOPBACK)) {
    err_offset = opt_iter;
    goto validate_return_locked;
    }



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