samples/seccomp: Support programs with >256 instructions
Previously, the program size was incorrectly truncated to 8 bits,
resulting in broken labels in large programs. Also changes the jump
resolution loop to not rely on undefined behavior (making a pointer
point before the filter array).
Signed-off-by: Ricky Zhou <rickyz@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
index 05cb4d5..1ef0f4d 100644
--- a/samples/seccomp/bpf-helper.c
+++ b/samples/seccomp/bpf-helper.c
@@ -18,41 +18,41 @@
int bpf_resolve_jumps(struct bpf_labels *labels,
struct sock_filter *filter, size_t count)
{
- struct sock_filter *begin = filter;
- __u8 insn = count - 1;
+ size_t i;
- if (count < 1)
+ if (count < 1 || count > BPF_MAXINSNS)
return -1;
/*
* Walk it once, backwards, to build the label table and do fixups.
* Since backward jumps are disallowed by BPF, this is easy.
*/
- filter += insn;
- for (; filter >= begin; --insn, --filter) {
- if (filter->code != (BPF_JMP+BPF_JA))
+ for (i = 0; i < count; ++i) {
+ size_t offset = count - i - 1;
+ struct sock_filter *instr = &filter[offset];
+ if (instr->code != (BPF_JMP+BPF_JA))
continue;
- switch ((filter->jt<<8)|filter->jf) {
+ switch ((instr->jt<<8)|instr->jf) {
case (JUMP_JT<<8)|JUMP_JF:
- if (labels->labels[filter->k].location == 0xffffffff) {
+ if (labels->labels[instr->k].location == 0xffffffff) {
fprintf(stderr, "Unresolved label: '%s'\n",
- labels->labels[filter->k].label);
+ labels->labels[instr->k].label);
return 1;
}
- filter->k = labels->labels[filter->k].location -
- (insn + 1);
- filter->jt = 0;
- filter->jf = 0;
+ instr->k = labels->labels[instr->k].location -
+ (offset + 1);
+ instr->jt = 0;
+ instr->jf = 0;
continue;
case (LABEL_JT<<8)|LABEL_JF:
- if (labels->labels[filter->k].location != 0xffffffff) {
+ if (labels->labels[instr->k].location != 0xffffffff) {
fprintf(stderr, "Duplicate label use: '%s'\n",
- labels->labels[filter->k].label);
+ labels->labels[instr->k].label);
return 1;
}
- labels->labels[filter->k].location = insn;
- filter->k = 0; /* fall through */
- filter->jt = 0;
- filter->jf = 0;
+ labels->labels[instr->k].location = offset;
+ instr->k = 0; /* fall through */
+ instr->jt = 0;
+ instr->jf = 0;
continue;
}
}
