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SubjectRe: [PATCH v3 3/7] kprobes: validate the symbol name length
On Wed, 19 Apr 2017 18:21:02 +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.

Would we really need this? Of course it may filter out longer
strings... anyway such name should be rejected by kallsyms.

[...]
> 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)

This just check the length of symbol_name buffer, and can contain
some invalid chars.

> +{
> + size_t sym_len;
> + char *s;
> +
> + s = strchr(name, ':');
> + if (s) {
> + sym_len = strnlen(s+1, KSYM_NAME_LEN);

If you use strnlen() here, you just need to ensure sym_len < 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)

Would you mean KSYM_NAME_LEN here?

> + 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.
> @@ -1397,6 +1419,8 @@ 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
>

Thanks,

--
Masami Hiramatsu <mhiramat@kernel.org>

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