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Subject[PATCH] samples/seccomp: improve label helper
Fixes a potential corruption with uninitialized stack memory in the seccomp
BPF sample program.

Reported-by: Robert Swiecki <swiecki@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
samples/seccomp/bpf-fancy.c | 4 +++-
samples/seccomp/bpf-helper.c | 5 +++++
2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/samples/seccomp/bpf-fancy.c b/samples/seccomp/bpf-fancy.c
index 8eb483aaec46..e8b24f443709 100644
--- a/samples/seccomp/bpf-fancy.c
+++ b/samples/seccomp/bpf-fancy.c
@@ -25,7 +25,9 @@

int main(int argc, char **argv)
{
- struct bpf_labels l;
+ struct bpf_labels l = {
+ .count = 0,
+ };
static const char msg1[] = "Please type something: ";
static const char msg2[] = "You typed: ";
char buf[256];
diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
index 579cfe331886..f9fa14d81798 100644
--- a/samples/seccomp/bpf-helper.c
+++ b/samples/seccomp/bpf-helper.c
@@ -10,6 +10,7 @@
*/

#include <stdio.h>
+#include <stdlib.h>
#include <string.h>

#include "bpf-helper.h"
@@ -63,6 +64,10 @@ __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
{
struct __bpf_label *begin = labels->labels, *end;
int id;
+ if (labels->count == BPF_LABELS_MAX) {
+ fprintf(stderr, "Too many labels\n");
+ exit(1);
+ }
if (labels->count == 0) {
begin->label = label;
begin->location = 0xffffffff;
--
1.9.1

--
Kees Cook
Chrome OS Security


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