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    SubjectRe: [BUGFIX] kprobes: prevent re-registration of the same kprobe - take2
    On Mon, Sep 14, 2009 at 12:25:41PM -0400, Masami Hiramatsu wrote:
    > Ananth N Mavinakayanahalli wrote:
    >> On Sun, Sep 13, 2009 at 09:47:39PM -0400, Masami Hiramatsu wrote:
    >>> Ananth N Mavinakayanahalli wrote:
    >>>> On Fri, Sep 11, 2009 at 05:12:54AM +0200, Frederic Weisbecker wrote:
    >>>>> On Thu, Sep 10, 2009 at 07:53:30PM -0400, Masami Hiramatsu wrote:

    ...

    >> +static inline int check_kprobe_rereg(struct kprobe *p)
    >> +{
    >> + int ret = 0;
    >> + struct kprobe *old_p;
    >> +
    >> + mutex_lock(&kprobe_mutex);
    >> + old_p = __get_valid_kprobe(p);
    >> + if (old_p == p)
    >
    > Here, since __get_valid_kprobe(p) will return aggr_kprobe of 'p',
    > you just need to check old_p != NULL.

    Right!

    ---
    Prevent re-registration of the same kprobe. This situation, though
    unlikely, needs to be flagged since it can lead to a system crash if its
    not handled.
    The core change itself is small, but the helper routine needed to be
    moved around a bit; hence the diffstat.

    Signed-off-by: Ananth N Mavinakayanahalli<ananth@in.ibm.com>
    ---
    kernel/kprobes.c | 58 ++++++++++++++++++++++++++++++++++++-------------------
    1 file changed, 38 insertions(+), 20 deletions(-)
    Index: linux-2.6.31/kernel/kprobes.c
    ===================================================================
    --- linux-2.6.31.orig/kernel/kprobes.c
    +++ linux-2.6.31/kernel/kprobes.c
    @@ -681,6 +681,40 @@ static kprobe_opcode_t __kprobes *kprobe
    return (kprobe_opcode_t *)(((char *)addr) + p->offset);
    }

    +/* Check passed kprobe is valid and return kprobe in kprobe_table. */
    +static struct kprobe * __kprobes __get_valid_kprobe(struct kprobe *p)
    +{
    + struct kprobe *old_p, *list_p;
    +
    + old_p = get_kprobe(p->addr);
    + if (unlikely(!old_p))
    + return NULL;
    +
    + if (p != old_p) {
    + list_for_each_entry_rcu(list_p, &old_p->list, list)
    + if (list_p == p)
    + /* kprobe p is a valid probe */
    + goto valid;
    + return NULL;
    + }
    +valid:
    + return old_p;
    +}
    +
    +/* Return error if the kprobe is being re-registered */
    +static inline int check_kprobe_rereg(struct kprobe *p)
    +{
    + int ret = 0;
    + struct kprobe *old_p;
    +
    + mutex_lock(&kprobe_mutex);
    + old_p = __get_valid_kprobe(p);
    + if (old_p)
    + ret = -EINVAL;
    + mutex_unlock(&kprobe_mutex);
    + return ret;
    +}
    +
    int __kprobes register_kprobe(struct kprobe *p)
    {
    int ret = 0;
    @@ -693,6 +727,10 @@ int __kprobes register_kprobe(struct kpr
    return -EINVAL;
    p->addr = addr;

    + ret = check_kprobe_rereg(p);
    + if (ret)
    + return ret;
    +
    preempt_disable();
    if (!kernel_text_address((unsigned long) p->addr) ||
    in_kprobes_functions((unsigned long) p->addr)) {
    @@ -762,26 +800,6 @@ out:
    }
    EXPORT_SYMBOL_GPL(register_kprobe);

    -/* Check passed kprobe is valid and return kprobe in kprobe_table. */
    -static struct kprobe * __kprobes __get_valid_kprobe(struct kprobe *p)
    -{
    - struct kprobe *old_p, *list_p;
    -
    - old_p = get_kprobe(p->addr);
    - if (unlikely(!old_p))
    - return NULL;
    -
    - if (p != old_p) {
    - list_for_each_entry_rcu(list_p, &old_p->list, list)
    - if (list_p == p)
    - /* kprobe p is a valid probe */
    - goto valid;
    - return NULL;
    - }
    -valid:
    - return old_p;
    -}
    -
    /*
    * Unregister a kprobe without a scheduler synchronization.
    */

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