linux-kernel - Re: [PATCH v3 3/7] kprobes: validate the symbol name length

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Message-ID: <87o9vr4nm3.fsf@concordia.ellerman.id.au>
Date:   Thu, 20 Apr 2017 16:08:52 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/7] kprobes: validate the symbol name length

"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> writes:

> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 6a128f3a7ed1..bb86681c8a10 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1382,6 +1382,28 @@ bool within_kprobe_blacklist(unsigned long addr)
>  	return false;
>  }
>  
> +bool is_valid_kprobe_symbol_name(const char *name)
> +{
> +	size_t sym_len;
> +	char *s;
> +
> +	s = strchr(name, ':');
> +	if (s) {
> +		sym_len = strnlen(s+1, KSYM_NAME_LEN);
> +		if (sym_len <= 0 || sym_len >= KSYM_NAME_LEN)
> +			return false;
> +		sym_len = (size_t)(s - name);
> +		if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
> +			return false;
> +	} else {
> +		sym_len = strnlen(name, MODULE_NAME_LEN);
> +		if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
> +			return false;
> +	}

I think this is probably more elaborate than it needs to be.

Why not just check the string is <= (MODULE_NAME_LEN + KSYM_NAME_LEN) ?

cheers