Re: [PATCH v2] coccinelle: free: add a checker for `__cleanup(kfree)` usage

[Julia Lawall]

On Thu, 24 Sep 2026, Ella Ma wrote:

> Using __cleanup(kfree) will pass the stack address of the annotated
> local variable to kfree functions. This will lead to invalid
> deallocation issues. Inspired by CVE-2026-45959 and similar bugs
> recently detected.

Thanks for the semantic patch.
I think it would be good for the error reports to be more explicit about
what the issue is, ie the relationship to the presence of absence of
DEFINE_FREE.  Otherwise, it is hard to completely understand the problem
without looking at the comments in the semantic patch.

julia

>
> Signed-off-by: Ella Ma <alansnape3058@xxxxxxxxx>
> ---
>
> Changes in v2:
> - Add virtual rules `report` and `org` as suggested by Sashiko
> - Remove `kvfree_sensitive` from rule `cleanup` as suggested by Sashiko
> - Add `free_percpu` to rule `free`
> - Add `kfree_const` to rule `cleanup`
>
> Currently, the five functions in the `free` rule are all the functions
> of `void (*)(const? void *)` type with a `DEFINE_FREE` definition in the
> code base. So I adopted all of them.
> Function `kfree_const` is added as it is of the kfree family and used
> more frequently than other kfree-family functions (even more frequently
> than some of those having a `DEFINE_FREE` definition).
> https://elixir.bootlin.com/linux/v7.3-rc3/A/ident/kfree_const
> (found in 64 files in v7.3-rc3).
>
> This cocci script can report the bug fixed in
> https://lore.kernel.org/lkml/20260617142632.3298984-1-vulab@xxxxxxxxxxx/
>
>  scripts/coccinelle/free/cleanup-free.cocci | 112 +++++++++++++++++++++
>  1 file changed, 112 insertions(+)
>  create mode 100644 scripts/coccinelle/free/cleanup-free.cocci
>
> diff --git a/scripts/coccinelle/free/cleanup-free.cocci b/scripts/coccinelle/free/cleanup-free.cocci
> new file mode 100644
> index 000000000000..63216ec5d865
> --- /dev/null
> +++ b/scripts/coccinelle/free/cleanup-free.cocci
> @@ -0,0 +1,112 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +///
> +/// Find __cleanup(kfree)
> +/// Using __cleanup(kfree) will pass the stack address of the annotated
> +/// local variable to kfree, causing an invalid free.
> +/// I.e., `T v __cleanup(kfree);` --> `kfree(&v);`
> +/// Such usage is impossible to be correct.
> +///
> +// Confidence: High
> +// Copyright: (C) 2026 Ella Ma
> +// Options: --no-includes --include-headers
> +
> +virtual report
> +virtual org
> +
> +// Suggesting using __free for the functions with a DEFINE_FREE definition.
> +// Update this list when new DEFINE_FREE definitions are added.
> +@free@
> +attribute name __cleanup;
> +symbol kfree, kfree_sensitive, kvfree, kvfree_atomic, free_percpu;
> +type T;
> +identifier v, n;
> +position p;
> +@@
> +
> +(
> +  T v __cleanup@p(
> +(
> +  n
> +&
> +(
> +  kfree \| kfree_sensitive \| kvfree \| kvfree_atomic \| free_percpu
> +)
> +)
> +  );
> +|
> +  T v __cleanup@p(
> +(
> +  n
> +&
> +(
> +  kfree \| kfree_sensitive \| kvfree \| kvfree_atomic \| free_percpu
> +)
> +)
> +  ) = ...;
> +)
> +
> +@script:python depends on report@
> +p << free.p;
> +n << free.n;
> +@@
> +
> +coccilib.report.print_report(
> +  p[0], f"ERROR: found `__cleanup({n})', do you mean `__free({n})'?")
> +
> +@script:python depends on org@
> +p << free.p;
> +n << free.n;
> +@@
> +
> +coccilib.org.print_todo(
> +  p[0], f"ERROR: found `__cleanup({n})', do you mean `__free({n})'?")
> +
> +
> +// Reporting __cleanup usage for the functions without a DEFINE_FREE definition.
> +// The following list only contains frequently used functions. Supplement it if
> +// necessary.
> +@cleanup@
> +attribute name __cleanup;
> +symbol vfree, vfree_atomic, kfree_const;
> +type T;
> +identifier v, n;
> +position p;
> +@@
> +
> +(
> +  T v __cleanup@p(
> +(
> +  n
> +&
> +(
> +  vfree \| vfree_atomic \| kfree_const
> +)
> +)
> +  );
> +|
> +  T v __cleanup@p(
> +(
> +  n
> +&
> +(
> +  vfree \| vfree_atomic \| kfree_const
> +)
> +)
> +  ) = ...;
> +)
> +
> +@script:python depends on report@
> +p << cleanup.p;
> +n << cleanup.n;
> +@@
> +
> +coccilib.report.print_report(
> +  p[0], f"ERROR: `__cleanup({n})' will free the annotated variable, rather than its pointee")
> +
> +@script:python depends on org@
> +p << cleanup.p;
> +n << cleanup.n;
> +@@
> +
> +coccilib.org.print_todo(
> +  p[0], f"ERROR: `__cleanup({n})' will free the annotated variable, rather than its pointee")
> --
> 2.34.1
>
>