bpf, net: Introduce skb_pointer_if_linear().

Network drivers always call skb_header_pointer() with non-null buffer.
Remove !buffer check to prevent accidental misuse of skb_header_pointer().
Introduce skb_pointer_if_linear() instead.

Reported-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230718234021.43640-1-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index ed83f1c..faaba05 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4023,7 +4023,7 @@ __skb_header_pointer(const struct sk_buff *skb, int offset, int len,
        if (likely(hlen - offset >= len))
                return (void *)data + offset;
 
-       if (!skb || !buffer || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))
+       if (!skb || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))
                return NULL;
 
        return buffer;
@@ -4036,6 +4036,14 @@ skb_header_pointer(const struct sk_buff *skb, int offset, int len, void *buffer)
                                    skb_headlen(skb), buffer);
 }
 
+static inline void * __must_check
+skb_pointer_if_linear(const struct sk_buff *skb, int offset, int len)
+{
+       if (likely(skb_headlen(skb) - offset >= len))
+               return skb->data + offset;
+       return NULL;
+}
+
 /**
  *     skb_needs_linearize - check if we need to linearize a given skb
  *                           depending on the given device features.

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index bcff584..56ce500 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2263,7 +2263,10 @@ __bpf_kfunc void *bpf_dynptr_slice(const struct bpf_dynptr_kern *ptr, u32 offset
        case BPF_DYNPTR_TYPE_RINGBUF:
                return ptr->data + ptr->offset + offset;
        case BPF_DYNPTR_TYPE_SKB:
-               return skb_header_pointer(ptr->data, ptr->offset + offset, len, buffer__opt);
+               if (buffer__opt)
+                       return skb_header_pointer(ptr->data, ptr->offset + offset, len, buffer__opt);
+               else
+                       return skb_pointer_if_linear(ptr->data, ptr->offset + offset, len);
        case BPF_DYNPTR_TYPE_XDP:
        {
                void *xdp_ptr = bpf_xdp_pointer(ptr->data, ptr->offset + offset, len);