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    Subject[ 148/153] kmod: make __request_module() killable
    3.2-stable review patch.  If anyone has any objections, please let me know.

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

    From: Oleg Nesterov <oleg@redhat.com>

    commit 1cc684ab75123efe7ff446eb821d44375ba8fa30 upstream.

    As Tetsuo Handa pointed out, request_module() can stress the system
    while the oom-killed caller sleeps in TASK_UNINTERRUPTIBLE.

    The task T uses "almost all" memory, then it does something which
    triggers request_module(). Say, it can simply call sys_socket(). This
    in turn needs more memory and leads to OOM. oom-killer correctly
    chooses T and kills it, but this can't help because it sleeps in
    TASK_UNINTERRUPTIBLE and after that oom-killer becomes "disabled" by the
    TIF_MEMDIE task T.

    Make __request_module() killable. The only necessary change is that
    call_modprobe() should kmalloc argv and module_name, they can't live in
    the stack if we use UMH_KILLABLE. This memory is freed via
    call_usermodehelper_freeinfo()->cleanup.

    Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    kernel/kmod.c | 26 ++++++++++++++++++++++++--
    1 file changed, 24 insertions(+), 2 deletions(-)

    --- a/kernel/kmod.c
    +++ b/kernel/kmod.c
    @@ -58,6 +58,12 @@ static DEFINE_SPINLOCK(umh_sysctl_lock);
    */
    char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";

    +static void free_modprobe_argv(struct subprocess_info *info)
    +{
    + kfree(info->argv[3]); /* check call_modprobe() */
    + kfree(info->argv);
    +}
    +
    static int call_modprobe(char *module_name, int wait)
    {
    static char *envp[] = {
    @@ -67,10 +73,26 @@ static int call_modprobe(char *module_na
    NULL
    };

    - char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
    + char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
    + if (!argv)
    + goto out;
    +
    + module_name = kstrdup(module_name, GFP_KERNEL);
    + if (!module_name)
    + goto free_argv;
    +
    + argv[0] = modprobe_path;
    + argv[1] = "-q";
    + argv[2] = "--";
    + argv[3] = module_name; /* check free_modprobe_argv() */
    + argv[4] = NULL;

    return call_usermodehelper_fns(modprobe_path, argv, envp,
    - wait, NULL, NULL, NULL);
    + wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
    +free_argv:
    + kfree(argv);
    +out:
    + return -ENOMEM;
    }

    /**



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