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    SubjectRe: PROBLEM: tun/tap crashes if open() /dev/net/tun and then poll() it.
    On Mon, 6 Jul 2009 09:12:30 +0800
    Herbert Xu <herbert@gondor.apana.org.au> wrote:

    > On Mon, Jul 06, 2009 at 12:11:14AM +0200, Mariusz Kozlowski wrote:
    > >
    > > Can you try this patch?
    ...
    > Good catch. Can you please resend with a sign-off?

    Sure. Just wanted to wait for confirmation from Eugene.

    Fix NULL pointer dereference in tun_chr_pool() introduced by
    commit 33dccbb050bbe35b88ca8cf1228dcf3e4d4b3554 and triggered
    by this code:

    int fd;
    struct pollfd pfd;
    fd = open("/dev/net/tun", O_RDWR);
    pfd.fd = fd;
    pfd.events = POLLIN | POLLOUT;
    poll(&pfd, 1, 0);

    Reported-by: Eugene Kapun <abacabadabacaba@gmail.com>
    Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>

    diff --git a/drivers/net/tun.c b/drivers/net/tun.c
    index a1b0697..bcbb25e 100644
    --- a/drivers/net/tun.c
    +++ b/drivers/net/tun.c
    @@ -482,12 +482,14 @@ static unsigned int tun_chr_poll(struct file *file, poll_table * wait)
    {
    struct tun_file *tfile = file->private_data;
    struct tun_struct *tun = __tun_get(tfile);
    - struct sock *sk = tun->sk;
    + struct sock *sk;
    unsigned int mask = 0;

    if (!tun)
    return POLLERR;

    + sk = tun->sk;
    +
    DBG(KERN_INFO "%s: tun_chr_poll\n", tun->dev->name);

    poll_wait(file, &tfile->read_wait, wait);


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