offload.c - make tether_error_map read only.
Bug: 254543135
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I5d4c9cad66f59bd7eed54323ba72ea5a54ddf5e1
diff --git a/bpf_progs/offload.c b/bpf_progs/offload.c
index bb9fc34..c7b444d 100644
--- a/bpf_progs/offload.c
+++ b/bpf_progs/offload.c
@@ -91,8 +91,11 @@
// ----- Tethering Error Counters -----
-DEFINE_BPF_MAP_GRW(tether_error_map, ARRAY, uint32_t, uint32_t, BPF_TETHER_ERR__MAX,
- TETHERING_GID)
+// Note that pre-T devices with Mediatek chipsets may have a kernel bug (bad patch
+// "[ALPS05162612] bpf: fix ubsan error") making it impossible to write to non-zero
+// offset of bpf map ARRAYs. This file (offload.o) loads on T, but luckily this
+// array is only written by bpf code, and only read by userspace.
+DEFINE_BPF_MAP_RO(tether_error_map, ARRAY, uint32_t, uint32_t, BPF_TETHER_ERR__MAX, TETHERING_GID)
#define COUNT_AND_RETURN(counter, ret) do { \
uint32_t code = BPF_TETHER_ERR_ ## counter; \