On Fri, 2026-03-06 at 22:44 -0800, Amery Hung wrote:

The verifier should decide whether a dynptr argument is read-only
based on if the type is "const struct bpf_dynptr *", not the type of
the register passed to the kfunc. This currently does not cause issues
because existing kfuncs that mutate struct bpf_dynptr are constructors
(e.g., bpf_dynptr_from_xxx and bpf_dynptr_clone). These kfuncs have
additional check in process_dynptr_func() to make sure the stack slot
does not contain initialized dynptr. Nonetheless, this should still be
fixed to avoid future issues when there is a non-constructor dynptr
kfunc that can mutate dynptr. This is also a small step toward unifying
kfunc and helper handling in the verifier, where the first step is to
generate kfunc prototype similar to bpf_func_proto before the main
verification loop.

We also need to correctly mark some kfunc arguments as "const struct
bpf_dynptr *" to align with other kfuncs that take non-mutable dynptr
argument and to not break their usage. Adding const qualifier does
not break backward compatibility.

Signed-off-by: Amery Hung <redacted>
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Acked-by: Eduard Zingerman <eddyz87@gmail.com>

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