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SubjectRe: [PATCH] Using a pointer and kzalloc in place of a struct directly
On Sat, Sep 12, 2020 at 05:08:04PM +0530, Anant Thazhemadam wrote:
> Updated the usage of a struct variable directly, in bpf_link_get_info_by_fd
> to using a pointer of the same type instead, which points to a memory
> location allocated using kzalloc.
>
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>

Note, your "To:" line seemed corrupted, and why not cc: the bpf mailing
list as well?

Anyway, comment on your patch below:

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 4108ef3b828b..01b9c203ef65 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3605,30 +3605,31 @@ static int bpf_link_get_info_by_fd(struct file *file,
> union bpf_attr __user *uattr)
> {
> struct bpf_link_info __user *uinfo = u64_to_user_ptr(attr->info.info);
> - struct bpf_link_info info;
> + struct bpf_link_info *info = NULL;
> u32 info_len = attr->info.info_len;
> int err;
>
> - err = bpf_check_uarg_tail_zero(uinfo, sizeof(info), info_len);
> + err = bpf_check_uarg_tail_zero(uinfo, sizeof(struct bpf_link_info), info_len);
> +
> if (err)
> return err;
> info_len = min_t(u32, sizeof(info), info_len);
>
> - memset(&info, 0, sizeof(info));
> - if (copy_from_user(&info, uinfo, info_len))
> + info = kzalloc(sizeof(struct bpf_link_info), GFP_KERNEL);
> + if (copy_from_user(info, uinfo, info_len))
> return -EFAULT;

You leaked memory :(

Did you test this patch? Where do you free this memory, I don't see
that happening anywhere in this patch, did I miss it?

And odds are this change will slow things down, right? Why make this
change, what's wrong with the structure being on the stack?

thanks,

greg k-h

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