linux-kernel - Re: [PATCH bpf v2 1/2] bpf: fix %p% runtime check in bpf_bprintf

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Message-ID: <CABRcYm+fR0qRk1FS8edB0zNFtg+GXt3vp025HU4eq-vCR52rRg@mail.gmail.com>
Date: Thu, 31 Oct 2024 17:17:42 +0100
From: Florent Revest <revest@...omium.org>
To: Yonghong Song <yonghong.song@...ux.dev>
Cc: Ilya Shchipletsov <rabbelkin@...l.ru>, bpf@...r.kernel.org, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Nikita Marushkin <hfggklm@...il.com>, lvc-project@...uxtesting.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf v2 1/2] bpf: fix %p% runtime check in bpf_bprintf_prepare

Acked-by: Florent Revest <revest@...omium.org>

On Tue, Oct 29, 2024 at 7:18 AM Yonghong Song <yonghong.song@...ux.dev> wrote:
>
>
> On 10/28/24 12:53 PM, Ilya Shchipletsov wrote:
> > Fuzzing reports a warning in format_decode()
> >
> > Please remove unsupported %� in format string
> > WARNING: CPU: 0 PID: 5091 at lib/vsprintf.c:2680 format_decode+0x1193/0x1bb0 lib/vsprintf.c:2680
> > Modules linked in:
> > CPU: 0 PID: 5091 Comm: syz-executor879 Not tainted 6.10.0-rc1-syzkaller-00021-ge0cce98fe279 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
> > RIP: 0010:format_decode+0x1193/0x1bb0 lib/vsprintf.c:2680
> > Call Trace:
> >   <TASK>
> >   bstr_printf+0x137/0x1210 lib/vsprintf.c:3253
> >   ____bpf_trace_printk kernel/trace/bpf_trace.c:390 [inline]
> >   bpf_trace_printk+0x1a1/0x230 kernel/trace/bpf_trace.c:375
> >   bpf_prog_21da1b68f62e1237+0x36/0x41
> >   bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
> >   __bpf_prog_run include/linux/filter.h:691 [inline]
> >   bpf_prog_run include/linux/filter.h:698 [inline]
> >   bpf_test_run+0x40b/0x910 net/bpf/test_run.c:425
> >   bpf_prog_test_run_skb+0xafa/0x13a0 net/bpf/test_run.c:1066
> >   bpf_prog_test_run+0x33c/0x3b0 kernel/bpf/syscall.c:4291
> >   __sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5705
> >   __do_sys_bpf kernel/bpf/syscall.c:5794 [inline]
> >   __se_sys_bpf kernel/bpf/syscall.c:5792 [inline]
> >   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5792
> >   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
> >   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > The problem occurs when trying to pass %p% at the end of format string,
> > which would result in skipping last % and passing invalid format string
> > down to format_decode() that would cause warning because of invalid
> > character after %.
> >
> > Fix issue by advancing pointer only if next char is format modifier.
> > If next char is null/space/punct, then just accept formatting as is,
> > without advancing the pointer.
> >
> > Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> >
> > Reported-by: syzbot+e2c932aec5c8a6e1d31c@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=e2c932aec5c8a6e1d31c
> > Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf")
> > Co-developed-by: Nikita Marushkin <hfggklm@...il.com>
> > Signed-off-by: Nikita Marushkin <hfggklm@...il.com>
> > Signed-off-by: Ilya Shchipletsov <rabbelkin@...l.ru>
>
> Acked-by: Yonghong Song <yonghong.song@...ux.dev>
>