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    Subject[094/107] drivers/misc/lkdtm.c: fix race when crashpoint is hit multiple times before checking count
    2.6.39-stable review patch.  If anyone has any objections, please let us know.

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

    From: Josh Hunt <johunt@akamai.com>

    commit aa2c96d6f329e66cc59352b0f12e8f04e6a9593b upstream.

    We observed the crash point count going negative in cases where the
    crash point is hit multiple times before the check of "count == 0" is
    done. Because of this we never call lkdtm_do_action(). This patch just
    adds a spinlock to protect count.

    Reported-by: Tapan Dhimant <tdhimant@akamai.com>
    Signed-off-by: Josh Hunt <johunt@akamai.com>
    Acked-by: Ankita Garg <ankita@in.ibm.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/misc/lkdtm.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    --- a/drivers/misc/lkdtm.c
    +++ b/drivers/misc/lkdtm.c
    @@ -120,6 +120,7 @@ static int recur_count = REC_NUM_DEFAULT
    static enum cname cpoint = CN_INVALID;
    static enum ctype cptype = CT_NONE;
    static int count = DEFAULT_COUNT;
    +static DEFINE_SPINLOCK(count_lock);

    module_param(recur_count, int, 0644);
    MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test, "\
    @@ -230,11 +231,14 @@ static const char *cp_name_to_str(enum c
    static int lkdtm_parse_commandline(void)
    {
    int i;
    + unsigned long flags;

    if (cpoint_count < 1 || recur_count < 1)
    return -EINVAL;

    + spin_lock_irqsave(&count_lock, flags);
    count = cpoint_count;
    + spin_unlock_irqrestore(&count_lock, flags);

    /* No special parameters */
    if (!cpoint_type && !cpoint_name)
    @@ -349,6 +353,9 @@ static void lkdtm_do_action(enum ctype w

    static void lkdtm_handler(void)
    {
    + unsigned long flags;
    +
    + spin_lock_irqsave(&count_lock, flags);
    count--;
    printk(KERN_INFO "lkdtm: Crash point %s of type %s hit, trigger in %d rounds\n",
    cp_name_to_str(cpoint), cp_type_to_str(cptype), count);
    @@ -357,6 +364,7 @@ static void lkdtm_handler(void)
    lkdtm_do_action(cptype);
    count = cpoint_count;
    }
    + spin_unlock_irqrestore(&count_lock, flags);
    }

    static int lkdtm_register_cpoint(enum cname which)



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