Re: [PATCH RESEND v3 4/4] perf_event_open: switch to copy_struct_from_user()

Kees Cook
2019-09-30T23:44:28Z

On Tue, Oct 01, 2019 at 05:15:26AM +1000, Aleksa Sarai wrote:
> From: Aleksa Sarai <cyphar@cyphar.com>
>
> The change is very straightforward, and helps unify the syscall
> interface for struct-from-userspace syscalls.
>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> kernel/events/core.c | 47 +++++++++-----------------------------------
> 1 file changed, 9 insertions(+), 38 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4655adbbae10..3f0cb82e4fbc 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10586,55 +10586,26 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
> u32 size;
> int ret;
>
> - if (!access_ok(uattr, PERF_ATTR_SIZE_VER0))
> - return -EFAULT;
> -
> - /*
> - * zero the full structure, so that a short copy will be nice.
> - */
> + /* Zero the full structure, so that a short copy will be nice. */
> memset(attr, 0, sizeof(*attr));
>
> ret = get_user(size, &uattr->size);
> if (ret)
> return ret;
>
> - if (size > PAGE_SIZE) /* silly large */
> - goto err_size;
> -
> - if (!size) /* abi compat */
> + /* ABI compatibility quirk: */
> + if (!size)
> size = PERF_ATTR_SIZE_VER0;
> -
> - if (size < PERF_ATTR_SIZE_VER0)
> + if (size < PERF_ATTR_SIZE_VER0 || size > PAGE_SIZE)
> goto err_size;
>
> - /*
> - * If we're handed a bigger struct than we know of,
> - * ensure all the unknown bits are 0 - i.e. new
> - * user-space does not rely on any kernel feature
> - * extensions we dont know about yet.
> - */
> - if (size > sizeof(*attr)) {
> - unsigned char __user *addr;
> - unsigned char __user *end;
> - unsigned char val;
> -
> - addr = (void __user *)uattr + sizeof(*attr);
> - end = (void __user *)uattr + size;
> -
> - for (; addr < end; addr++) {
> - ret = get_user(val, addr);
> - if (ret)
> - return ret;
> - if (val)
> - goto err_size;
> - }
> - size = sizeof(*attr);
> + ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
> + if (ret) {
> + if (ret == -E2BIG)
> + goto err_size;
> + return ret;
> }
>
> - ret = copy_from_user(attr, uattr, size);
> - if (ret)
> - return -EFAULT;
> -
> attr->size = size;
>
> if (attr->__reserved_1)
> --
> 2.23.0
>

--
Kees Cook