On Wed, 10 Apr 2024 09:58:02 +0800
Zheng Yejian <zhengyeji...@huawei.com> wrote:
> When unloading a module, its state is changing MODULE_STATE_LIVE ->
> MODULE_STATE_GOING -> MODULE_STATE_UNFORMED. Each change will take
> a time. `is_module_text_address()` and `__module_text_address()`
> works with MODULE_STATE_LIVE and MODULE_STATE_GOING.
> If we use `is_module_text_address()` and `__module_text_address()`
> separately, there is a chance that the first one is succeeded but the
> next one is failed because module->state becomes MODULE_STATE_UNFORMED
> between those operations.
>
> In `check_kprobe_address_safe()`, if the second `__module_text_address()`
> is failed, that is ignored because it expected a kernel_text address.
> But it may have failed simply because module->state has been changed
> to MODULE_STATE_UNFORMED. In this case, arm_kprobe() will try to modify
> non-exist module text address (use-after-free).
>
> To fix this problem, we should not use separated `is_module_text_address()`
> and `__module_text_address()`, but use only `__module_text_address()`
> once and do `try_module_get(module)` which is only available with
> MODULE_STATE_LIVE.
>
> Signed-off-by: Zheng Yejian <zhengyeji...@huawei.com>
Looks good to me. Let me pick this version, and it should be a bugfix.
Fixes: 28f6c37a2910 ("kprobes: Forbid probing on trampoline and BPF code areas")
Cc: sta...@vger.kernel.org
Thank you!
> ---
> kernel/kprobes.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> v3:
> - Update commit messages as suggested by Masami.
> Link:
> https://lore.kernel.org/all/20240409224922.5f192e8ace5f7a90937bf...@kernel.org/
> - Also change to a more appropriate title.
>
> v2:
> - Update commit messages and comments as suggested by Masami.
> Link:
> https://lore.kernel.org/all/20240408115038.b0c85767bf1f249eccc32...@kernel.org/
> - Link:
> https://lore.kernel.org/all/20240408083403.3302274-1-zhengyeji...@huawei.com/
>
> v1:
> - Link:
> https://lore.kernel.org/all/20240407035904.2556645-1-zhengyeji...@huawei.com/
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 9d9095e81792..65adc815fc6e 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1567,10 +1567,17 @@ static int check_kprobe_address_safe(struct kprobe *p,
> jump_label_lock();
> preempt_disable();
>
> - /* Ensure it is not in reserved area nor out of text */
> - if (!(core_kernel_text((unsigned long) p->addr) ||
> - is_module_text_address((unsigned long) p->addr)) ||
> - in_gate_area_no_mm((unsigned long) p->addr) ||
> + /* Ensure the address is in a text area, and find a module if exists. */
> + *probed_mod = NULL;
> + if (!core_kernel_text((unsigned long) p->addr)) {
> + *probed_mod = __module_text_address((unsigned long) p->addr);
> + if (!(*probed_mod)) {
> + ret = -EINVAL;
> + goto out;
> + }
> + }
> + /* Ensure it is not in reserved area. */
> + if (in_gate_area_no_mm((unsigned long) p->addr) ||
> within_kprobe_blacklist((unsigned long) p->addr) ||
> jump_label_text_reserved(p->addr, p->addr) ||
> static_call_text_reserved(p->addr, p->addr) ||
> @@ -1580,8 +1587,7 @@ static int check_kprobe_address_safe(struct kprobe *p,
> goto out;
> }
>
> - /* Check if 'p' is probing a module. */
> - *probed_mod = __module_text_address((unsigned long) p->addr);
> + /* Get module refcount and reject __init functions for loaded modules.
> */
> if (*probed_mod) {
> /*
> * We must hold a refcount of the probed module while updating
> --
> 2.25.1
>
--
Masami Hiramatsu (Google) <mhira...@kernel.org>
