Re: [PATCH 3/3] bpf: use copy_struct_from_user() in bpf() syscall

[Aleksa Sarai]

On 2019-10-09, Christian Brauner <christian.brauner@xxxxxxxxxx> wrote:
> In v5.4-rc2 we added a new helper (cf. [1]) copy_struct_from_user().
> This helper is intended for all codepaths that copy structs from
> userspace that are versioned by size. The bpf() syscall does exactly
> what copy_struct_from_user() is doing.
> Note that copy_struct_from_user() is calling min() already. So
> technically, the min_t() call could go. But the size is used further
> below so leave it.
> 
> [1]: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>

Acked-by: Aleksa Sarai <cyphar@xxxxxxxxxx>

> ---
>  kernel/bpf/syscall.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 6f4f9097b1fe..6fdcbdb27501 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2819,14 +2819,11 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
>  	if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
>  		return -EPERM;
>  
> -	err = bpf_check_uarg_tail_zero(uattr, sizeof(attr), size);
> -	if (err)
> -		return err;
>  	size = min_t(u32, size, sizeof(attr));
> -
>  	/* copy attributes from user space, may be less than sizeof(bpf_attr) */
> -	if (copy_from_user(&attr, uattr, size) != 0)
> -		return -EFAULT;
> +	err = copy_struct_from_user(&attr, sizeof(attr), uattr, size);
> +	if (err)
> +		return err;
>  
>  	err = security_bpf(cmd, &attr, size);
>  	if (err < 0)
> -- 
> 2.23.0

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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