Commit ac6542ad authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Alexei Starovoitov
Browse files

bpf: fix null dereference when computing changes_pkt_data of prog w/o subprogs 



bpf_prog_aux->func field might be NULL if program does not have
subprograms except for main sub-program. The fixed commit does
bpf_prog_aux->func access unconditionally, which might lead to null
pointer dereference.

The bug could be triggered by replacing the following BPF program:

    SEC("tc")
    int main_changes(struct __sk_buff *sk)
    {
        bpf_skb_pull_data(sk, 0);
        return 0;
    }

With the following BPF program:

    SEC("freplace")
    long changes_pkt_data(struct __sk_buff *sk)
    {
        return bpf_skb_pull_data(sk, 0);
    }

bpf_prog_aux instance itself represents the main sub-program,
use this property to fix the bug.

Fixes: 81f6d053 ("bpf: check changes_pkt_data property for extension programs")
Reported-by: default avatarkernel test robot <lkp@intel.com>
Reported-by: default avatarDan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202412111822.qGw6tOyB-lkp@intel.com/


Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20241212070711.427443-1-eddyz87@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 7d0d6736

kernel/bpf/verifier.c

+5 −2
Original line number Diff line number Diff line
@@ -22193,6 +22193,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, 
	}

	if (tgt_prog) {

		struct bpf_prog_aux *aux = tgt_prog->aux;

		bool tgt_changes_pkt_data;









		if (bpf_prog_is_dev_bound(prog->aux) &&









		    !bpf_prog_dev_bound_match(prog, tgt_prog)) {








@@ -22227,8 +22228,10 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,







					"Extension programs should be JITed\n");









				return -EINVAL;









			}









			if (prog->aux->changes_pkt_data &&









			    !aux->func[subprog]->aux->changes_pkt_data) {









			tgt_changes_pkt_data = aux->func









					       ? aux->func[subprog]->aux->changes_pkt_data









					       : aux->changes_pkt_data;









			if (prog->aux->changes_pkt_data && !tgt_changes_pkt_data) {









				bpf_log(log,









					"Extension program changes packet data, while original does not\n");









				return -EINVAL;