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    SubjectRe: [PATCH 1/1] threads_max: Simple lockout prevention patch
    Date
    This is a resend, which was ignored before w/o comment.
    A comment this time would be helpful. Thanks!

    -

    Simple attempt to provide a backdoor in a process lockout situation.

    echo $$ > /proc/sys/kernel/su-pid allows pid to exceed the threads_max limit.

    Signed-off-by: Al Boldi <a1426z@gawab.com>

    ---
    (patch against 2.6.14)

    --- kernel/fork.c.orig 2005-11-14 20:55:33.000000000 +0300
    +++ kernel/fork.c 2005-11-14 20:58:25.000000000 +0300
    @@ -57,6 +57,7 @@
    int nr_threads; /* The idle threads do not count.. */

    int max_threads; /* tunable limit on nr_threads */
    +int su_pid; /* BackDoor pid to exceed limit on nr_threads */

    DEFINE_PER_CPU(unsigned long, process_counts) = 0;

    @@ -926,6 +927,7 @@
    * to stop root fork bombs.
    */
    if (nr_threads >= max_threads)
    + if (p->pid != su_pid)
    goto bad_fork_cleanup_count;

    if (!try_module_get(p->thread_info->exec_domain->module))

    --- kernel/sysctl.c.orig 2005-11-14 20:58:45.000000000 +0300
    +++ kernel/sysctl.c 2005-11-14 21:01:20.000000000 +0300
    @@ -57,6 +57,7 @@
    extern int sysctl_overcommit_memory;
    extern int sysctl_overcommit_ratio;
    extern int max_threads;
    +extern int su_pid;
    extern int sysrq_enabled;
    extern int core_uses_pid;
    extern int suid_dumpable;
    @@ -509,6 +510,14 @@
    .proc_handler = &proc_dointvec,
    },
    {
    + .ctl_name = KERN_SU_PID,
    + .procname = "su-pid",
    + .data = &su_pid,
    + .maxlen = sizeof(int),
    + .mode = 0644,
    + .proc_handler = &proc_dointvec,
    + },
    + {
    .ctl_name = KERN_RANDOM,
    .procname = "random",
    .mode = 0555,

    --- include/linux/sysctl.h.orig 2005-11-14 20:54:55.000000000 +0300
    +++ include/linux/sysctl.h 2005-11-14 20:55:15.000000000 +0300
    @@ -146,6 +146,7 @@
    KERN_RANDOMIZE=68, /* int: randomize virtual address space */
    KERN_SETUID_DUMPABLE=69, /* int: behaviour of dumps for setuid core
    */
    KERN_SPIN_RETRY=70, /* int: number of spinlock retries */
    + KERN_SU_PID=71, /* int: BackDoor pid to exceed Maximum
    + /* nr of threads in the system */
    };


    -
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