From: Richard Weinberger <richard@nod.at>
To: Petr Mladek <pmladek@suse.com>
Cc: "Kees Cook" <keescook@chromium.org>,
linux-hardening <linux-hardening@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
"Steven Rostedt" <rostedt@goodmis.org>,
senozhatsky <senozhatsky@chromium.org>,
"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
davem <davem@davemloft.net>, edumazet <edumazet@google.com>,
kuba <kuba@kernel.org>, pabeni <pabeni@redhat.com>,
"Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Benno Lossin" <benno.lossin@proton.me>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Jesper Dangaard Brouer" <hawk@kernel.org>,
"John Fastabend" <john.fastabend@gmail.com>
Subject: Re: [RFC PATCH 0/1] Integer overflows while scanning for integers
Date: Thu, 8 Jun 2023 18:12:11 +0200 (CEST) [thread overview]
Message-ID: <520885538.3699431.1686240731083.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <ZIHzbBXlxEz6As9N@alley>
----- Ursprüngliche Mail -----
> Von: "Petr Mladek" <pmladek@suse.com>
> On Wed 2023-06-07 16:36:12, Kees Cook wrote:
>> On Thu, Jun 08, 2023 at 12:37:54AM +0200, Richard Weinberger wrote:
>> > Hi!
>> >
>> > Lately I wondered whether users of integer scanning functions check
>> > for overflows.
>> > To detect such overflows around scanf I came up with the following
>> > patch. It simply triggers a WARN_ON_ONCE() upon an overflow.
>> >
>> > After digging into various scanf users I found that the network device
>> > naming code can trigger an overflow.
>> >
>> > e.g:
>> > $ ip link add 1 type veth peer name 9999999999
>> > $ ip link set name "%d" dev 1
>> >
>> > It will trigger the following WARN_ON_ONCE():
>> > ------------[ cut here ]------------
>> > WARNING: CPU: 2 PID: 433 at lib/vsprintf.c:3701 vsscanf+0x6ce/0x990
>>
>> Hm, it's considered a bug if a WARN or BUG can be reached from
>> userspace,
>
> Good point. WARN() does not look like the right way in this case.
Well, the whole point of my RFC(!) patch is showing the issue and providing a way
to actually find such call sites, like the netdev code.
> Another problem is that some users use panic_on_warn. In this case,
> the above "ip" command calls would trigger panic(). And it does not
> look like an optimal behavior.
Only if we don't fix netdev code.
> I know there already are some WARN_ONs for similar situations, e.g.
> set_field_width() or set_precision(). But these do not get random
> values. And it would actually be nice to introduce something like
> INFO() that would be usable for these less serious problems where
> the backtrace is useful but they should never trigger panic().
>
>> so this probably needs to be rearranged (or callers fixed).
>> Do we need to change the scanf API for sane use inside the kernel?
>
> It seems that userspace implementation of sscanf() and vsscanf()
> returns -ERANGE in this case. It might be a reasonable solution.
>
> Well, there is a risk of introducing security problems. The error
> value might cause an underflow/overflow when the caller does not expect
> a negative value.
Agreed. Without inspecting all users of scanf we cannot change the API.
> Alternative solution would be to update the "ip" code so that it
> reads the number separately and treat zero return value as
> -EINVAL.
The kernel needs fixing, not userspace.
Thanks,
//richard
next prev parent reply other threads:[~2023-06-08 16:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-07 22:37 [RFC PATCH 0/1] Integer overflows while scanning for integers Richard Weinberger
2023-06-07 22:37 ` [RFC PATCH 1/1] vsprintf: Warn on integer scanning overflows Richard Weinberger
2023-06-08 14:27 ` Andy Shevchenko
2023-06-08 16:14 ` Richard Weinberger
2023-06-08 16:23 ` Andy Shevchenko
2023-06-12 6:16 ` kernel test robot
2023-06-07 23:36 ` [RFC PATCH 0/1] Integer overflows while scanning for integers Kees Cook
2023-06-08 15:27 ` Petr Mladek
2023-06-08 16:12 ` Richard Weinberger [this message]
2023-06-08 16:19 ` Greg KH
2023-06-08 16:23 ` Richard Weinberger
2023-06-09 10:10 ` Rasmus Villemoes
2023-06-09 17:02 ` Petr Mladek
2023-06-09 17:46 ` Linus Torvalds
2023-06-10 19:31 ` David Laight
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