From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
Ingo Molnar <mingo@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v3 3/7] kprobes: validate the symbol name length
Date: Wed, 19 Apr 2017 16:38:22 +0000 [thread overview]
Message-ID: <1492619420.q0fv2gslsy.astroid@naverao1-tp.none> (raw)
In-Reply-To: <20170419233750.8552f5de8ce1ed1398807284@kernel.org>
Excerpts from Masami Hiramatsu's message of April 19, 2017 20:07:
> 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.
I felt this would be good to have generically, as kallsyms does many
string operations on the symbol name, including an unbounded strchr().
>
> [...]
>> 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.
Yes, I kept the function name generic incase we would like to do more
validation in future, plus it's shorter than
is_valid_kprobe_symbol_name_len() ;-)
>
>> +{
>> + size_t sym_len;
>> + char *s;
>> +
>> + s = strchr(name, ':');
Hmm.. this should be strnchr(). I re-factored the code that moved the
strnlen() above this below. I'll fix this.
>> + 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.
Hmm.. not sure I follow. Are you saying the check for sym_len <= 0 is
not needed?
>
>> + 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?
Oops... nice catch, Thanks!
- Naveen
>
>> + 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>
>
>
next prev parent reply other threads:[~2017-04-19 16:39 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-19 12:50 [PATCH v3 0/7] powerpc: a few kprobe fixes and refactoring Naveen N. Rao
2017-04-19 12:51 ` [PATCH v3 1/7] kprobes: convert kprobe_lookup_name() to a function Naveen N. Rao
2017-04-24 22:47 ` [v3,1/7] " Michael Ellerman
2017-04-19 12:51 ` [PATCH v3 2/7] powerpc: kprobes: fix handling of function offsets on ABIv2 Naveen N. Rao
2017-04-24 22:47 ` [v3,2/7] " Michael Ellerman
2017-04-19 12:51 ` [PATCH v3 3/7] kprobes: validate the symbol name length Naveen N. Rao
2017-04-19 14:37 ` Masami Hiramatsu
2017-04-19 16:38 ` Naveen N. Rao [this message]
2017-04-21 13:42 ` Masami Hiramatsu
2017-04-23 15:44 ` Naveen N. Rao
2017-04-25 3:18 ` Masami Hiramatsu
2017-04-20 6:08 ` Michael Ellerman
2017-04-20 7:19 ` Naveen N. Rao
2017-04-21 12:32 ` [PATCH v4 3/7] kprobes: validate the symbol name provided during probe registration Naveen N. Rao
2017-04-21 13:11 ` Paul Clarke
2017-04-21 13:25 ` Naveen N. Rao
2017-04-21 13:54 ` Masami Hiramatsu
2017-04-22 5:55 ` Michael Ellerman
2017-04-23 17:41 ` Naveen N. Rao
2017-04-21 12:33 ` [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in kprobe_lookup_name() Naveen N. Rao
2017-04-21 13:33 ` Paul Clarke
2017-04-21 13:36 ` Paul Clarke
2017-04-21 13:52 ` Paul Clarke
2017-04-23 17:09 ` Naveen N. Rao
2017-04-19 12:51 ` [PATCH v3 4/7] powerpc: kprobes: use " Naveen N. Rao
2017-04-21 15:06 ` David Laight
2017-04-19 12:51 ` [PATCH v3 5/7] powerpc: kprobes: factor out code to emulate instruction into a helper Naveen N. Rao
2017-04-19 14:40 ` Masami Hiramatsu
2017-04-24 22:47 ` [v3, " Michael Ellerman
2017-04-19 12:51 ` [PATCH v3 6/7] powerpc: kprobes: emulate instructions on kprobe handler re-entry Naveen N. Rao
2017-04-19 14:43 ` Masami Hiramatsu
2017-04-19 16:42 ` Naveen N. Rao
2017-04-20 6:11 ` Michael Ellerman
2017-04-21 13:48 ` Masami Hiramatsu
2017-04-24 22:47 ` [v3, " Michael Ellerman
2017-04-19 12:51 ` [PATCH v3 7/7] powerpc: kprobes: remove duplicate saving of msr Naveen N. Rao
2017-04-19 14:43 ` Masami Hiramatsu
2017-04-23 11:53 ` [v3,7/7] " Michael Ellerman
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