| Message ID | 1401470112-3933-1-git-send-email-chema@google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On 05/30/2014 07:15 PM, Chema Gonzalez wrote: > 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 <chema@google.com> Thanks (sorry for the delay as I'm currently on travel). Acked-by: Daniel Borkmann <dborkman@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sat, May 31, 2014 at 12:21 PM, Daniel Borkmann <dborkman@redhat.com> wrote: > On 05/30/2014 07:15 PM, Chema Gonzalez wrote: >> >> 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 <chema@google.com> Thank you for addressing all our comments. Acked-by: Alexei Starovoitov <ast@plumgrid.com> > > Thanks (sorry for the delay as I'm currently on travel). > > Acked-by: Daniel Borkmann <dborkman@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Chema Gonzalez <chema@google.com> Date: Fri, 30 May 2014 10:15:12 -0700 > 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 <chema@google.com> Applied, thank you. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/lib/test_bpf.c b/lib/test_bpf.c index af677cb..e60f766 100644 --- a/lib/test_bpf.c +++ b/lib/test_bpf.c @@ -158,6 +158,18 @@ static struct bpf_test tests[] = { { { 0, 0x800000ff }, { 1, 0x800000ff } }, }, { + "LD_IMM_0", + .u.insns = { + BPF_STMT(BPF_LD | BPF_IMM, 0), /* ld #0 */ + BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 1, 0), + BPF_STMT(BPF_RET | BPF_K, 0), + BPF_STMT(BPF_RET | BPF_K, 1), + }, + CLASSIC, + { }, + { { 1, 1 } }, + }, + { "LD_IND", .u.insns = { BPF_STMT(BPF_LDX | BPF_LEN, 0), @@ -1542,12 +1554,11 @@ static int probe_filter_length(struct sock_filter *fp) { int len = 0; - while (fp->code != 0 || fp->k != 0) { - fp++; - len++; - } + for (len = MAX_INSNS - 1; len > 0; --len) + if (fp[len].code != 0 || fp[len].k != 0) + break; - return len; + return len + 1; } static struct sk_filter *generate_filter(int which, int *err)
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 <chema@google.com> --- lib/test_bpf.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)