Commit 8e8ee109 authored by Florent Revest's avatar Florent Revest Committed by Alexei Starovoitov
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bpf: Notify user if we ever hit a bpf_snprintf verifier bug 



In check_bpf_snprintf_call(), a map_direct_value_addr() of the fmt map
should never fail because it has already been checked by
ARG_PTR_TO_CONST_STR. But if it ever fails, it's better to error out
with an explicit debug message rather than silently fail.

Reported-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarFlorent Revest <revest@chromium.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210422235543.4007694-2-revest@chromium.org
parent e7a1c130

kernel/bpf/verifier.c

+4 −2
Original line number Diff line number Diff line
@@ -5940,8 +5940,10 @@ static int check_bpf_snprintf_call(struct bpf_verifier_env *env, 
	fmt_map_off = fmt_reg->off + fmt_reg->var_off.value;

	err = fmt_map->ops->map_direct_value_addr(fmt_map, &fmt_addr,

						  fmt_map_off);

	if (err)

		return err;

	if (err) {

		verbose(env, "verifier bug\n");

		return -EFAULT;

	}

	fmt = (char *)(long)fmt_addr + fmt_map_off;



	/* We are also guaranteed that fmt+fmt_map_off is NULL terminated, we