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    Subject[34-longterm 188/196] taskstats: don't allow duplicate entries in listener mode
    Date
    From: Vasiliy Kulikov <segoon@openwall.com>

    -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
    -------------------

    commit 26c4caea9d697043cc5a458b96411b86d7f6babd upstream.

    Currently a single process may register exit handlers unlimited times.
    It may lead to a bloated listeners chain and very slow process
    terminations.

    Eg after 10KK sent TASKSTATS_CMD_ATTR_REGISTER_CPUMASKs ~300 Mb of
    kernel memory is stolen for the handlers chain and "time id" shows 2-7
    seconds instead of normal 0.003. It makes it possible to exhaust all
    kernel memory and to eat much of CPU time by triggerring numerous exits
    on a single CPU.

    The patch limits the number of times a single process may register
    itself on a single CPU to one.

    One little issue is kept unfixed - as taskstats_exit() is called before
    exit_files() in do_exit(), the orphaned listener entry (if it was not
    explicitly deregistered) is kept until the next someone's exit() and
    implicit deregistration in send_cpu_listeners(). So, if a process
    registered itself as a listener exits and the next spawned process gets
    the same pid, it would inherit taskstats attributes.

    Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
    Cc: Balbir Singh <bsingharora@gmail.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    kernel/taskstats.c | 15 ++++++++++++---
    1 file changed, 12 insertions(+), 3 deletions(-)

    diff --git a/kernel/taskstats.c b/kernel/taskstats.c
    index 11281d5..5e21645 100644
    --- a/kernel/taskstats.c
    +++ b/kernel/taskstats.c
    @@ -292,16 +292,18 @@ ret:
    static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
    {
    struct listener_list *listeners;
    - struct listener *s, *tmp;
    + struct listener *s, *tmp, *s2;
    unsigned int cpu;

    if (!cpumask_subset(mask, cpu_possible_mask))
    return -EINVAL;

    + s = NULL;
    if (isadd == REGISTER) {
    for_each_cpu(cpu, mask) {
    - s = kmalloc_node(sizeof(struct listener), GFP_KERNEL,
    - cpu_to_node(cpu));
    + if (!s)
    + s = kmalloc_node(sizeof(struct listener),
    + GFP_KERNEL, cpu_to_node(cpu));
    if (!s)
    goto cleanup;
    s->pid = pid;
    @@ -310,9 +312,16 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)

    listeners = &per_cpu(listener_array, cpu);
    down_write(&listeners->sem);
    + list_for_each_entry_safe(s2, tmp, &listeners->list, list) {
    + if (s2->pid == pid)
    + goto next_cpu;
    + }
    list_add(&s->list, &listeners->list);
    + s = NULL;
    +next_cpu:
    up_write(&listeners->sem);
    }
    + kfree(s);
    return 0;
    }

    --
    1.7.9.3


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