[bpf,0/4] bpf: track changes_pkt_data property for global functions

Message

Eduard Zingerman Dec. 6, 2024, 4:03 a.m. UTC

Nick Zavaritsky reported [0] a bug in verifier, where the following
unsafe program is not rejected:

    __attribute__((__noinline__))
    long skb_pull_data(struct __sk_buff *sk, __u32 len)
    {
        return bpf_skb_pull_data(sk, len);
    }

    SEC("tc")
    int test_invalidate_checks(struct __sk_buff *sk)
    {
        int *p = (void *)(long)sk->data;
        if ((void *)(p + 1) > (void *)(long)sk->data_end) return TCX_DROP;
        skb_pull_data(sk, 0);
        /* not safe, p is invalid after bpf_skb_pull_data call */
        *p = 42;
        return TCX_PASS;
    }

This happens because verifier does not track package invalidation
effect of global sub-programs.

This patch-set fixes the issue by modifying check_cfg() to compute
whether or not each sub-program calls (directly or indirectly)
helper invalidating packet pointers.

[0] https://lore.kernel.org/bpf/[e-mail]/

Eduard Zingerman (4):
  bpf: add find_containing_subprog() utility function
  bpf: refactor bpf_helper_changes_pkt_data to use helper number
  bpf: track changes_pkt_data property for global functions
  selftests/bpf: test for changing packet data from global functions

 include/linux/bpf_verifier.h                  |  1 +
 include/linux/filter.h                        |  2 +-
 kernel/bpf/core.c                             |  2 +-
 kernel/bpf/verifier.c                         | 62 ++++++++++++++++--
 net/core/filter.c                             | 63 +++++++++----------
 .../selftests/bpf/progs/verifier_sock.c       | 28 +++++++++
 6 files changed, 115 insertions(+), 43 deletions(-)