Commit d58e468b1112 ("flow_dissector: implements flow dissector BPF
hook") added direct packet access for skbs in may_access_direct_pkt_data()
function where this enables read and write access to the skb->data. This
is buggy because without a prologue generator such as bpf_unclone_prologue()
we would allow for writing into cloned skbs. Original intention might have
been to only allow read access where this is not needed (similar as the
flow_dissector_func_proto() indicates which enables only bpf_skb_load_bytes()
as well), therefore this patch fixes it to restrict to read-only.
Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Cc: Petar Penkov <[email protected]>
---
kernel/bpf/verifier.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 98fa0be..b0cc8f2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1387,21 +1387,23 @@ static bool may_access_direct_pkt_data(struct
bpf_verifier_env *env,
enum bpf_access_type t)
{
switch (env->prog->type) {
+ /* Program types only with direct read access go here! */
case BPF_PROG_TYPE_LWT_IN:
case BPF_PROG_TYPE_LWT_OUT:
case BPF_PROG_TYPE_LWT_SEG6LOCAL:
case BPF_PROG_TYPE_SK_REUSEPORT:
- /* dst_input() and dst_output() can't write for now */
+ case BPF_PROG_TYPE_FLOW_DISSECTOR:
if (t == BPF_WRITE)
return false;
/* fallthrough */
+
+ /* Program types with direct read + write access go here! */
case BPF_PROG_TYPE_SCHED_CLS:
case BPF_PROG_TYPE_SCHED_ACT:
case BPF_PROG_TYPE_XDP:
case BPF_PROG_TYPE_LWT_XMIT:
case BPF_PROG_TYPE_SK_SKB:
case BPF_PROG_TYPE_SK_MSG:
- case BPF_PROG_TYPE_FLOW_DISSECTOR:
if (meta)
return meta->pkt_access;
--
2.9.5
