From: Kees Cook <keescook@chromium.org>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] atags_proc: Add __counted_by for struct buffer and use struct_size()
Date: Tue, 10 Oct 2023 16:09:35 -0700 [thread overview]
Message-ID: <202310101607.3D7ED0A@keescook> (raw)
In-Reply-To: <ZSVHurzo/4aFQcT3@work>
On Tue, Oct 10, 2023 at 06:46:50AM -0600, Gustavo A. R. Silva wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
>
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
>
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> arch/arm/kernel/atags_proc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kernel/atags_proc.c b/arch/arm/kernel/atags_proc.c
> index 3ec2afe78423..cd09f8ab93e3 100644
> --- a/arch/arm/kernel/atags_proc.c
> +++ b/arch/arm/kernel/atags_proc.c
> @@ -7,7 +7,7 @@
>
> struct buffer {
> size_t size;
> - char data[];
> + char data[] __counted_by(size);
> };
>
> static ssize_t atags_read(struct file *file, char __user *buf,
> @@ -54,7 +54,7 @@ static int __init init_atags_procfs(void)
>
> WARN_ON(tag->hdr.tag != ATAG_NONE);
>
> - b = kmalloc(sizeof(*b) + size, GFP_KERNEL);
> + b = kmalloc(struct_size(b, data, size), GFP_KERNEL);
> if (!b)
> goto nomem;
>
Yup, "size" is assigned before accessing "data".
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2023-10-10 23:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-10 12:46 [PATCH][next] atags_proc: Add __counted_by for struct buffer and use struct_size() Gustavo A. R. Silva
2023-10-10 17:58 ` Justin Stitt
2023-10-10 23:09 ` Kees Cook [this message]
2023-12-02 20:32 ` Kees Cook
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