• Alexei Starovoitov's avatar
    bpf: allow extended BPF programs access skb fields · 9bac3d6d
    Alexei Starovoitov authored
    introduce user accessible mirror of in-kernel 'struct sk_buff':
    struct __sk_buff {
        __u32 len;
        __u32 pkt_type;
        __u32 mark;
        __u32 queue_mapping;
    };
    
    bpf programs can do:
    
    int bpf_prog(struct __sk_buff *skb)
    {
        __u32 var = skb->pkt_type;
    
    which will be compiled to bpf assembler as:
    
    dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type)
    
    bpf verifier will check validity of access and will convert it to:
    
    dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset))
    dst_reg &= 7
    
    since skb->pkt_type is a bitfield.
    Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9bac3d6d
verifier.c 58.4 KB