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    Subject[PATCH 6.0 330/862] mISDN: fix use-after-free bugs in l1oip timer handlers
    Date
    From: Duoming Zhou <duoming@zju.edu.cn>

    [ Upstream commit 2568a7e0832ee30b0a351016d03062ab4e0e0a3f ]

    The l1oip_cleanup() traverses the l1oip_ilist and calls
    release_card() to cleanup module and stack. However,
    release_card() calls del_timer() to delete the timers
    such as keep_tl and timeout_tl. If the timer handler is
    running, the del_timer() will not stop it and result in
    UAF bugs. One of the processes is shown below:

    (cleanup routine) | (timer handler)
    release_card() | l1oip_timeout()
    ... |
    del_timer() | ...
    ... |
    kfree(hc) //FREE |
    | hc->timeout_on = 0 //USE

    Fix by calling del_timer_sync() in release_card(), which
    makes sure the timer handlers have finished before the
    resources, such as l1oip and so on, have been deallocated.

    What's more, the hc->workq and hc->socket_thread can kick
    those timers right back in. We add a bool flag to show
    if card is released. Then, check this flag in hc->workq
    and hc->socket_thread.

    Fixes: 3712b42d4b1b ("Add layer1 over IP support")
    Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
    Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/isdn/mISDN/l1oip.h | 1 +
    drivers/isdn/mISDN/l1oip_core.c | 13 +++++++------
    2 files changed, 8 insertions(+), 6 deletions(-)

    diff --git a/drivers/isdn/mISDN/l1oip.h b/drivers/isdn/mISDN/l1oip.h
    index 7ea10db20e3a..48133d022812 100644
    --- a/drivers/isdn/mISDN/l1oip.h
    +++ b/drivers/isdn/mISDN/l1oip.h
    @@ -59,6 +59,7 @@ struct l1oip {
    int bundle; /* bundle channels in one frm */
    int codec; /* codec to use for transmis. */
    int limit; /* limit number of bchannels */
    + bool shutdown; /* if card is released */

    /* timer */
    struct timer_list keep_tl;
    diff --git a/drivers/isdn/mISDN/l1oip_core.c b/drivers/isdn/mISDN/l1oip_core.c
    index 2c40412466e6..a77195e378b7 100644
    --- a/drivers/isdn/mISDN/l1oip_core.c
    +++ b/drivers/isdn/mISDN/l1oip_core.c
    @@ -275,7 +275,7 @@ l1oip_socket_send(struct l1oip *hc, u8 localcodec, u8 channel, u32 chanmask,
    p = frame;

    /* restart timer */
    - if (time_before(hc->keep_tl.expires, jiffies + 5 * HZ))
    + if (time_before(hc->keep_tl.expires, jiffies + 5 * HZ) && !hc->shutdown)
    mod_timer(&hc->keep_tl, jiffies + L1OIP_KEEPALIVE * HZ);
    else
    hc->keep_tl.expires = jiffies + L1OIP_KEEPALIVE * HZ;
    @@ -601,7 +601,9 @@ l1oip_socket_parse(struct l1oip *hc, struct sockaddr_in *sin, u8 *buf, int len)
    goto multiframe;

    /* restart timer */
    - if (time_before(hc->timeout_tl.expires, jiffies + 5 * HZ) || !hc->timeout_on) {
    + if ((time_before(hc->timeout_tl.expires, jiffies + 5 * HZ) ||
    + !hc->timeout_on) &&
    + !hc->shutdown) {
    hc->timeout_on = 1;
    mod_timer(&hc->timeout_tl, jiffies + L1OIP_TIMEOUT * HZ);
    } else /* only adjust timer */
    @@ -1232,11 +1234,10 @@ release_card(struct l1oip *hc)
    {
    int ch;

    - if (timer_pending(&hc->keep_tl))
    - del_timer(&hc->keep_tl);
    + hc->shutdown = true;

    - if (timer_pending(&hc->timeout_tl))
    - del_timer(&hc->timeout_tl);
    + del_timer_sync(&hc->keep_tl);
    + del_timer_sync(&hc->timeout_tl);

    cancel_work_sync(&hc->workq);

    --
    2.35.1


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