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bpf: Notify user if we ever hit a bpf_snprintf verifier bug

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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: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210422235543.4007694-2-revest@chromium.org
This commit is contained in:
Florent Revest 2021-04-23 01:55:42 +02:00 committed by Alexei Starovoitov
parent e7a1c13008
commit 8e8ee109b0
1 changed files with 4 additions and 2 deletions
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6
kernel/bpf/verifier.c
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@ -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