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SubjectRe: [PATCH v4 3/7] kprobes: validate the symbol name provided during probe registration
On Fri, 21 Apr 2017 18:02:33 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> When a kprobe is being registered, we use the symbol_name field to
> lookup the address where the probe should be placed. Since this is a
> user-provided field, let's ensure that the length of the string is
> within expected limits.
>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> Masami, Michael,
> Here's a simplified version that should hopefully be fine. I have
> simplified the logic to keep the code compact and simple.

Ok, so as I replied to older version,
- Ensure name != NULL at first.
- Define it in kernel/kallsyms.c as a general routine.

Since this validate the string which will be passed to kallsyms,
I think it should be provided by kallsyms.

Thanks,

>
> - Naveen
>
>
> include/linux/kprobes.h | 1 +
> kernel/kprobes.c | 30 ++++++++++++++++++++++++++++++
> kernel/trace/trace_kprobe.c | 4 ++++
> 3 files changed, 35 insertions(+)
>
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 1f82a3db00b1..4ee10fef5135 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -405,6 +405,7 @@ int disable_kprobe(struct kprobe *kp);
> int enable_kprobe(struct kprobe *kp);
>
> void dump_kprobe(struct kprobe *kp);
> +bool is_valid_kprobe_symbol_name(const char *name);
>
> #else /* !CONFIG_KPROBES: */
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 6a128f3a7ed1..ff9b1ac72a38 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1383,6 +1383,34 @@ bool within_kprobe_blacklist(unsigned long addr)
> }
>
> /*
> + * We mainly want to ensure that the provided string is of a reasonable length
> + * and is of the form [<mod_name>:]<sym_name>, so that this is safe to process
> + * further.
> + * We don't worry about invalid characters as those will just prevent
> + * matching existing kallsyms.
> + */
> +bool is_valid_kprobe_symbol_name(const char *name)
> +{
> + size_t sym_len;
> + const char *s;
> +
> + s = strnchr(name, ':', MODULE_NAME_LEN + KSYM_NAME_LEN + 1);
> + if (s) {
> + sym_len = (size_t)(s - name);
> + if (sym_len <= 0 || sym_len >= MODULE_NAME_LEN)
> + return false;
> + s++;
> + } else
> + s = name;
> +
> + sym_len = strnlen(s, KSYM_NAME_LEN);
> + if (sym_len <= 0 || sym_len >= KSYM_NAME_LEN)
> + return false;
> +
> + return true;
> +}
> +
> +/*
> * If we have a symbol_name argument, look it up and add the offset field
> * to it. This way, we can specify a relative address to a symbol.
> * This returns encoded errors if it fails to look up symbol or invalid
> @@ -1397,6 +1425,8 @@ static kprobe_opcode_t *kprobe_addr(struct kprobe *p)
> goto invalid;
>
> if (p->symbol_name) {
> + if (!is_valid_kprobe_symbol_name(p->symbol_name))
> + return ERR_PTR(-EINVAL);
> addr = kprobe_lookup_name(p->symbol_name, p->offset);
> if (!addr)
> return ERR_PTR(-ENOENT);
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 5f688cc724f0..bf73e5f31128 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -704,6 +704,10 @@ static int create_trace_kprobe(int argc, char **argv)
> pr_info("Return probe must be used without offset.\n");
> return -EINVAL;
> }
> + if (!is_valid_kprobe_symbol_name(symbol)) {
> + pr_info("Symbol name is too long.\n");
> + return -EINVAL;
> + }
> }
> argc -= 2; argv += 2;
>
> --
> 2.12.1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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