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net: filter: fix length calculation in BPF testsuite

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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>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Chema Gonzalez 2014-05-30 10:15:12 -07:00 committed by David S. Miller
parent f7b4e71c9d
commit e9d9450497
1 changed files with 16 additions and 5 deletions
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21
lib/test_bpf.c
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@ -157,6 +157,18 @@ 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 = {
@ -1734,12 +1746,11 @@ 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)