Re: [PATCH 7/9] Simplify bound checks in capabilities for copy_from_user

James Morris
2009-10-01T22:35:42Z

On Tue, 29 Sep 2009, Arjan van de Ven wrote:

> From: Arjan van de Ven <arjan@linux.intel.com>
> Subject: [PATCH 7/9] Simplify bound checks in capabilities for copy_from_user
> CC: James Morris <jmorris@namei.org>
>
> The capabilities syscall has a copy_from_user() call where gcc currently
> cannot prove to itself that the copy is always within bounds.
>
> This patch adds a very explicity bound check to prove to gcc that
> this copy_from_user cannot overflow its destination buffer.
>
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

Acked-by: James Morris <jmorris@namei.org>

> diff --git a/kernel/capability.c b/kernel/capability.c
> index 4e17041..204f11f 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -238,7 +241,7 @@ SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
> SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
> {
> struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
> - unsigned i, tocopy;
> + unsigned i, tocopy, copybytes;
> kernel_cap_t inheritable, permitted, effective;
> struct cred *new;
> int ret;
> @@ -255,8 +258,11 @@ SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
> if (pid != 0 && pid != task_pid_vnr(current))
> return -EPERM;
>
> - if (copy_from_user(&kdata, data,
> - tocopy * sizeof(struct __user_cap_data_struct)))
> + copybytes = tocopy * sizeof(struct __user_cap_data_struct);
> + if (copybytes > sizeof(kdata))
> + return -EFAULT;
> +
> + if (copy_from_user(&kdata, data, copybytes))
> return -EFAULT;
>
> for (i = 0; i < tocopy; i++) {
>
>
>
> --
> Arjan van de Ven Intel Open Source Technology Centre
> For development, discussion and tips for power savings,
> visit http://www.lesswatts.org
>

--
James Morris
<jmorris@namei.org>