Message ID | 1401391757-27620-1-git-send-email-chema@google.com |
---|---|
State | Superseded, archived |
Delegated to: | David Miller |
Headers | show |
On 05/29/2014 09:29 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> Looks good to me, thanks a lot Chema! Acked-by: Daniel Borkmann <dborkman@redhat.com> > + for (len = MAX_INSNS-1; len > 0; --len) > + if (fp[len].code != 0 || fp[len].k != 0) > + break; > > - return len; > + return len+1; Nit: would be great to have a whitespace between MAX_INSNS-1 and len+1 but that shouldn't matter that much, perhaps. -- 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 Thu, May 29, 2014 at 1:41 PM, Daniel Borkmann <dborkman@redhat.com> wrote: > On 05/29/2014 09:29 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> > > > Looks good to me, thanks a lot Chema! > > Acked-by: Daniel Borkmann <dborkman@redhat.com> > > >> + for (len = MAX_INSNS-1; len > 0; --len) >> + if (fp[len].code != 0 || fp[len].k != 0) >> + break; >> >> - return len; >> + return len+1; > > > Nit: would be great to have a whitespace between MAX_INSNS-1 and len+1 but > that shouldn't matter that much, perhaps. Done. -Chema -- 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..e893e3b 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(-)