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: 81f6d0530ba0 ("bpf: check changes_pkt_data property for extension programs")
Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]/
Signed-off-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

0 files changed, 0 insertions, 0 deletions