On Thu, Dec 8, 2016 at 11:48 AM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> wrote:
> kmod_concurrent is used as an atomic counter for enabling
> the allowed limit of modprobe calls, provide wrappers for it
> to enable this to be expanded on more easily. This will be done
> later.
>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> ---
> kernel/kmod.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/kmod.c b/kernel/kmod.c
> index cb6f7ca7b8a5..049d7eabda38 100644
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -44,6 +44,9 @@
> #include <trace/events/module.h>
>
> extern int max_threads;
> +
> +static atomic_t kmod_concurrent = ATOMIC_INIT(0);
> +
> unsigned int max_modprobes;
> module_param(max_modprobes, uint, 0644);
> MODULE_PARM_DESC(max_modprobes, "Max number of allowed concurrent modprobes");
> @@ -108,6 +111,20 @@ static int call_modprobe(char *module_name, int wait)
> return -ENOMEM;
> }
>
> +static int kmod_umh_threads_get(void)
> +{
> + atomic_inc(&kmod_concurrent);
> + if (atomic_read(&kmod_concurrent) < max_modprobes)
> + return 0;
> + atomic_dec(&kmod_concurrent);
> + return -ENOMEM;
> +}
> +
> +static void kmod_umh_threads_put(void)
> +{
> + atomic_dec(&kmod_concurrent);
> +}
Can you use a kref here instead? We're trying to kill raw use of
atomic_t for reference counting...
> +
> /**
> * __request_module - try to load a kernel module
> * @wait: wait (or not) for the operation to complete
> @@ -129,7 +146,6 @@ int __request_module(bool wait, const char *fmt, ...)
> va_list args;
> char module_name[MODULE_NAME_LEN];
> int ret;
> - static atomic_t kmod_concurrent = ATOMIC_INIT(0);
> static int kmod_loop_msg;
>
> /*
> @@ -153,8 +169,8 @@ int __request_module(bool wait, const char *fmt, ...)
> if (ret)
> return ret;
>
> - atomic_inc(&kmod_concurrent);
> - if (atomic_read(&kmod_concurrent) > max_modprobes) {
> + ret = kmod_umh_threads_get();
> + if (ret) {
> /* We may be blaming an innocent here, but unlikely */
> if (kmod_loop_msg < 5) {
> printk(KERN_ERR
> @@ -162,15 +178,14 @@ int __request_module(bool wait, const char *fmt, ...)
> module_name);
> kmod_loop_msg++;
> }
> - atomic_dec(&kmod_concurrent);
> - return -ENOMEM;
> + return ret;
> }
>
> trace_module_request(module_name, wait, _RET_IP_);
>
> ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
>
> - atomic_dec(&kmod_concurrent);
> + kmod_umh_threads_put();
> return ret;
> }
> EXPORT_SYMBOL(__request_module);
> --
> 2.10.1
>
--
Kees Cook
Nexus Security
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