[PATCH bpf v2 2/3] bpf: zero out build_id for BPF_STACK_BUILD_ID_IP

[Stanislav Fomichev <sdf@google.com>]

When returning BPF_STACK_BUILD_ID_IP from stack_map_get_build_id_offset,
make sure that build_id field is empty. Since we are using percpu
free list, there is a possibility that we might reuse some previous
bpf_stack_build_id with non-zero build_id.

Fixes: 615755a77b24 ("bpf: extend stackmap to save binary_build_id+offset instead of address")
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 kernel/bpf/stackmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index f9df545e92f6..d43b14535827 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -314,6 +314,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 		for (i = 0; i < trace_nr; i++) {
 			id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 			id_offs[i].ip = ips[i];
+			memset(id_offs[i].build_id, 0, BPF_BUILD_ID_SIZE);
 		}
 		return;
 	}
@@ -324,6 +325,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 			/* per entry fall back to ips */
 			id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 			id_offs[i].ip = ips[i];
+			memset(id_offs[i].build_id, 0, BPF_BUILD_ID_SIZE);
 			continue;
 		}
 		id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
-- 
2.20.1.97.g81188d93c3-goog