Re: [PATCH 1/2] scripts/coccinelle: catch freeing cryptographic structures via kfree

Julia Lawall
2014-11-17T15:31:01Z

On Mon, 17 Nov 2014, Konstantin Khlebnikov wrote:

> Structures allocated by crypto_alloc_* must be freed using crypto_free_*.
>
> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
> ---
> scripts/coccinelle/free/crypto_free.cocci | 45 +++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
> create mode 100644 scripts/coccinelle/free/crypto_free.cocci
>
> diff --git a/scripts/coccinelle/free/crypto_free.cocci b/scripts/coccinelle/free/crypto_free.cocci
> new file mode 100644
> index 0000000..0799b70
> --- /dev/null
> +++ b/scripts/coccinelle/free/crypto_free.cocci
> @@ -0,0 +1,45 @@
> +///
> +/// Structures allocated by crypto_alloc_* must be freed using crypto_free_*.
> +/// This finds freeing them by kfree.
> +///
> +// Confidence: Moderate
> +// Copyright: (C) 2014 Konstantin Khlebnikov, GPLv2.
> +// Comments: There are false positives in crypto/ where they are actually freed.
> +// Keywords: crypto, kfree
> +// Options: --no-includes --include-headers
> +
> +virtual org
> +virtual report
> +virtual context
> +
> +@r depends on context || org || report@
> +expression x;
> +identifier crypto_alloc =~ "^crypto_alloc_";
> +@@
> +
> +(
> + x = crypto_alloc(...)
> +)

You can drop the outer parentheses, in this case and in the kfree case.

Are there many of these crypto_alloc_ functions? It would be nicer to
avoid the regular expression. For one thing, you don't have much control
over what it matches, and for another thing Coccinelle will not be able to
optimize the selection of files. With the regular expression it will have
to parse every file and analyze every function, which will be slow.

julia

> +
> +@pb@
> +expression r.x;
> +position p;
> +@@
> +
> +(
> +* kfree@p(x)
> +)
> +
> +@script:python depends on org@
> +p << pb.p;
> +@@
> +
> +msg="WARNING: invalid free of crypto_alloc_* allocated data"
> +coccilib.org.print_todo(p[0], msg)
> +
> +@script:python depends on report@
> +p << pb.p;
> +@@
> +
> +msg="WARNING: invalid free of crypto_alloc_* allocated data"
> +coccilib.report.print_report(p[0], msg)
>
>