From f1692ee23dcaaddc24ba407b269707ee5df1301f Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Wed, 30 Apr 2025 16:19:49 +0800 Subject: [PATCH] bpf: consider that tail calls invalidate packet pointers commit 1a4607ffba35bf2a630aab299e34dd3f6e658d70 upstream. Tail-called programs could execute any of the helpers that invalidate packet pointers. Hence, conservatively assume that each tail call invalidates packet pointers. Making the change in bpf_helper_changes_pkt_data() automatically makes use of check_cfg() logic that computes 'changes_pkt_data' effect for global sub-programs, such that the following program could be rejected: int tail_call(struct __sk_buff *sk) { bpf_tail_call_static(sk, &jmp_table, 0); return 0; } SEC("tc") int not_safe(struct __sk_buff *sk) { int *p = (void *)(long)sk->data; ... make p valid ... tail_call(sk); *p = 42; /* this is unsafe */ ... } The tc_bpf2bpf.c:subprog_tc() needs change: mark it as a function that can invalidate packet pointers. Otherwise, it can't be freplaced with tailcall_freplace.c:entry_freplace() that does a tail call. Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20241210041100.1898468-8-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov [ shung-hsi.yu: drop changes to tools/testing/selftests/bpf/progs/tc_bpf2bpf.c because it is not present. ] Signed-off-by: Shung-Hsi Yu Signed-off-by: Greg Kroah-Hartman --- net/core/filter.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index 1127ab198409..c4c27e03279c 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -7893,6 +7893,8 @@ bool bpf_helper_changes_pkt_data(enum bpf_func_id func_id) case BPF_FUNC_xdp_adjust_head: case BPF_FUNC_xdp_adjust_meta: case BPF_FUNC_xdp_adjust_tail: + /* tail-called program could call any of the above */ + case BPF_FUNC_tail_call: return true; default: return false;