linux-kernel - Re: [PATCH v2 1/2] alloc_tag: add sequence number for module and iterator

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Message-ID: <CAJuCfpGa2UxLY5Af_R6ZR4q57T0380bAWvwYWv2PzC=0sgCqKQ@mail.gmail.com>
Date: Fri, 9 May 2025 12:25:47 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: David Wang <00107082@....com>
Cc: kent.overstreet@...ux.dev, akpm@...ux-foundation.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] alloc_tag: add sequence number for module and iterator

On Fri, May 9, 2025 at 10:39 AM David Wang <00107082@....com> wrote:
>
> Codetag iterator use <id,address> pair to guarantee the
> validness. But both id and address can be reused, there is
> theoretical possibility when module inserted right after
> another module removed, kmalloc returns an address same as
> the address kfree by previous module and IDR key reuses
> the key recently removed.
>
> Add a sequence number to codetag_module and code_iterator,
> the sequence number is strickly incremented whenever a module
> is loaded. An iterator is valid if and only if its sequence
> number match codetag_module's.
>
> Signed-off-by: David Wang <00107082@....com>

Acked-by: Suren Baghdasaryan <surenb@...gle.com>

> ---
>  include/linux/codetag.h |  1 +
>  lib/codetag.c           | 17 ++++++++++++++---
>  2 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/codetag.h b/include/linux/codetag.h
> index d14dbd26b370..90f707c3821f 100644
> --- a/include/linux/codetag.h
> +++ b/include/linux/codetag.h
> @@ -54,6 +54,7 @@ struct codetag_iterator {
>         struct codetag_module *cmod;
>         unsigned long mod_id;
>         struct codetag *ct;
> +       unsigned long mod_seq;
>  };
>
>  #ifdef MODULE
> diff --git a/lib/codetag.c b/lib/codetag.c
> index 42aadd6c1454..496cef7cdad3 100644
> --- a/lib/codetag.c
> +++ b/lib/codetag.c
> @@ -11,8 +11,14 @@ struct codetag_type {
>         struct list_head link;
>         unsigned int count;
>         struct idr mod_idr;
> -       struct rw_semaphore mod_lock; /* protects mod_idr */
> +       /*
> +        * protects mod_idr, next_mod_seq,
> +        * iter->mod_seq and cmod->mod_seq
> +        */
> +       struct rw_semaphore mod_lock;
>         struct codetag_type_desc desc;
> +       /* generates unique sequence number for module load */
> +       unsigned long next_mod_seq;
>  };
>
>  struct codetag_range {
> @@ -23,6 +29,7 @@ struct codetag_range {
>  struct codetag_module {
>         struct module *mod;
>         struct codetag_range range;
> +       unsigned long mod_seq;
>  };
>
>  static DEFINE_MUTEX(codetag_lock);
> @@ -48,6 +55,7 @@ struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
>                 .cmod = NULL,
>                 .mod_id = 0,
>                 .ct = NULL,
> +               .mod_seq = 0,
>         };
>
>         return iter;
> @@ -91,11 +99,13 @@ struct codetag *codetag_next_ct(struct codetag_iterator *iter)
>                 if (!cmod)
>                         break;
>
> -               if (cmod != iter->cmod) {
> +               if (!iter->cmod || iter->mod_seq != cmod->mod_seq) {
>                         iter->cmod = cmod;
> +                       iter->mod_seq = cmod->mod_seq;
>                         ct = get_first_module_ct(cmod);
> -               } else
> +               } else {
>                         ct = get_next_module_ct(iter);
> +               }
>
>                 if (ct)
>                         break;
> @@ -190,6 +200,7 @@ static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
>         cmod->range = range;
>
>         down_write(&cttype->mod_lock);
> +       cmod->mod_seq = ++cttype->next_mod_seq;
>         err = idr_alloc(&cttype->mod_idr, cmod, 0, 0, GFP_KERNEL);
>         if (err >= 0) {
>                 cttype->count += range_size(cttype, &range);
> --
> 2.39.2
>