On Sat, May 31, 2014 at 12:21 PM, Daniel Borkmann [off-list ref] wrote:

On 05/30/2014 07:15 PM, Chema Gonzalez wrote:

quoted

The current probe_filter_length() (the function that calculates the
length of a test BPF filter) behavior is to declare the end of the
filter as soon as it finds {0, *, *, 0}. This is actually a valid
insn ("ld #0"), so any filter with includes "BPF_STMT(BPF_LD | BPF_IMM,
0)"
fails (its length is cut short).

We are changing probe_filter_length() so as to start from the end, and
declare the end of the filter as the first instruction which is not
{0, *, *, 0}. This solution produces a simpler patch than the
alternative of using an explicit end-of-filter mark. It is technically
incorrect if your filter ends up with "ld #0", but that should not
happen anyway.

We also add a new test (LD_IMM_0) that includes ld #0 (does not work
without this patch).

Signed-off-by: Chema Gonzalez <redacted>

Thank you for addressing all our comments.

Acked-by: Alexei Starovoitov <redacted>

Thanks (sorry for the delay as I'm currently on travel).

Acked-by: Daniel Borkmann <redacted>