Re: [PATCH] bpf: explicitly memset the bpf_attr structure

On Fri, Mar 20, 2020 at 08:23:57AM -0700, Yonghong Song wrote:

On 3/20/20 2:48 AM, Greg Kroah-Hartman wrote:

quoted

For the bpf syscall, we are relying on the compiler to properly zero out
the bpf_attr union that we copy userspace data into.  Unfortunately that
doesn't always work properly, padding and other oddities might not be
correctly zeroed, and in some tests odd things have been found when the
stack is pre-initialized to other values.

Maybe add more contexts about the failure itself so it could be clear
why we need this patch.

I didn't have the full details, I think Maciej has them though.

As far as I know from the link below, the failure happens in
CHECK_ATTR() which checks any unused *area* for a particular subcommand
must be 0, and this patch tries to provide this guarantee beyond
area beyond min(uattr_size, sizeof(attr)).

That macro also will get tripped up if padding is not zeroed out as
well, so this is good to fix up.

thanks for the review.

greg k-h