Documentation: prctl/seccomp_filter

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / samples / seccomp / bpf-helper.c

diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
new file mode 100644 (file)
index 0000000..579cfe3
--- /dev/null
+++ b/samples/seccomp/bpf-helper.c
@@ -0,0 +1,89 @@
+/*
+ * Seccomp BPF helper functions
+ *
+ * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * Author: Will Drewry <wad@chromium.org>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "bpf-helper.h"
+
+int bpf_resolve_jumps(struct bpf_labels *labels,
+                     struct sock_filter *filter, size_t count)
+{
+       struct sock_filter *begin = filter;
+       __u8 insn = count - 1;
+
+       if (count < 1)
+               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))
+                       continue;
+               switch ((filter->jt<<8)|filter->jf) {
+               case (JUMP_JT<<8)|JUMP_JF:
+                       if (labels->labels[filter->k].location == 0xffffffff) {
+                               fprintf(stderr, "Unresolved label: '%s'\n",
+                                       labels->labels[filter->k].label);
+                               return 1;
+                       }
+                       filter->k = labels->labels[filter->k].location -
+                                   (insn + 1);
+                       filter->jt = 0;
+                       filter->jf = 0;
+                       continue;
+               case (LABEL_JT<<8)|LABEL_JF:
+                       if (labels->labels[filter->k].location != 0xffffffff) {
+                               fprintf(stderr, "Duplicate label use: '%s'\n",
+                                       labels->labels[filter->k].label);
+                               return 1;
+                       }
+                       labels->labels[filter->k].location = insn;
+                       filter->k = 0; /* fall through */
+                       filter->jt = 0;
+                       filter->jf = 0;
+                       continue;
+               }
+       }
+       return 0;
+}
+
+/* Simple lookup table for labels. */
+__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
+{
+       struct __bpf_label *begin = labels->labels, *end;
+       int id;
+       if (labels->count == 0) {
+               begin->label = label;
+               begin->location = 0xffffffff;
+               labels->count++;
+               return 0;
+       }
+       end = begin + labels->count;
+       for (id = 0; begin < end; ++begin, ++id) {
+               if (!strcmp(label, begin->label))
+                       return id;
+       }
+       begin->label = label;
+       begin->location = 0xffffffff;
+       labels->count++;
+       return id;
+}
+
+void seccomp_bpf_print(struct sock_filter *filter, size_t count)
+{
+       struct sock_filter *end = filter + count;
+       for ( ; filter < end; ++filter)
+               printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
+                       filter->code, filter->jt, filter->jf, filter->k);
+}