From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5526F1CC173 for ; Mon, 14 Oct 2024 21:29:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728941351; cv=none; b=pWdQeLOcb99rH9EtQTm/iR4rSpx/Q66itkOlwcALe6T0Yz75D/RT/1bpcOkyfPum1fNwKsiv69ojnkEN0amCRlLHioa+0eIcGlKVqyB14eA9QJRHidBEfxwg40ToKji+8MmcN2raa9kja4FzyliPX5FZXMGb6jgALPKpJvxflZ0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728941351; c=relaxed/simple; bh=+Fc5ELzw9cgbeRfJfp6d6rq0NL1HERYLDqAlzClUUlE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=d6HrhNcwA7ZMdZkM+7rp5iorSHfSSTbxWgTqyVmaTbsNfv/eKGisZnU8Tra3L7HHgqsi0CVgPgbZtCE8WbnpBtDTx6Wpe24nbM6ypl1hfWn0zPjA2dL5N9OsWc7ycOjraIHLYsWmk6bvjzksR4qTIYEqorOFEFJvAkbo1zJgEz4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=jgqrMoIQ; arc=none smtp.client-ip=91.218.175.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="jgqrMoIQ" Message-ID: <06260b1f-7fce-446f-9b06-309001bdae58@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1728941346; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=X2a/12gQx2FXChpTRAlFQ1e3CeEIxB8iEuXXSpY+6VI=; b=jgqrMoIQqaF1pLbSzpjBtMFN0/JXD7YVcGDTTvm+Fnce8KRDkP1lD/IvkLN9NGnuT787Pi NEhNzIM2IAWTqHrIK/LB8BfsxDr7/GHW1IpryuRHEX/xya1TjGSzxhH15eaIWRnfNmFifd WXbp0sbYzxB4e9DT6VnsNhsYoAIcT+g= Date: Mon, 14 Oct 2024 14:28:59 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf] bpf: fix %p% runtime check in bpf_bprintf_prepare Content-Language: en-GB To: Ilya Shchipletsov , bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , linux-kernel@vger.kernel.org, Florent Revest , Nikita Marushkin , lvc-project@linuxtesting.org References: <9679a031-3858-4fef-bb8e-1cf436696095@mail.ru> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <9679a031-3858-4fef-bb8e-1cf436696095@mail.ru> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 10/9/24 3:57 AM, 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: > > 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 %. Indeed, in kernel doing printk("%p%"); will have following compilation failure. /home/yhs/work/bpf-next/kernel/bpf/helpers.c:830:10: error: more '%' conversions than data arguments [-Werror,-Wformat-insufficient-args] 830 | printk("%p%"); | ~^ /home/yhs/work/bpf-next/include/linux/printk.h:490:53: note: expanded from macro 'printk' 490 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__) | ^~~ /home/yhs/work/bpf-next/include/linux/printk.h:462:11: note: expanded from macro 'printk_index_wrap' 462 | _p_func(_fmt, ##__VA_ARGS__); \ | ^~~~ 1 error generated. > > 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. > > Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf") > Co-developed-by: Nikita Marushkin > Signed-off-by: Nikita Marushkin > Signed-off-by: Ilya Shchipletsov LGTM with some comments and nits below. Acked-by: Yonghong Song > --- > kernel/bpf/helpers.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index c9e235807cac..bd771d6aacdb 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -892,14 +892,19 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args, > goto fmt_str; > } > > + if (fmt[i + 1] == 'K' || fmt[i + 1] == 'x' || > + fmt[i + 1] == 's' || fmt[i + 1] == 'S') { > + if (tmp_buf) > + cur_arg = raw_args[num_spec]; > + i++; > + goto nocopy_fmt; > + } > + > if (fmt[i + 1] == 0 || isspace(fmt[i + 1]) || > - ispunct(fmt[i + 1]) || fmt[i + 1] == 'K' || > - fmt[i + 1] == 'x' || fmt[i + 1] == 's' || > - fmt[i + 1] == 'S') { > + ispunct(fmt[i + 1])) { > /* just kernel pointers */ > if (tmp_buf) > cur_arg = raw_args[num_spec]; > - i++; > goto nocopy_fmt; > } We could do ispunct(fmt[i + 1]) only in the above 'if' statement. But your implementation is right too and maybe cleaner, so let us keep your above implementation. Could you move comment '/* just kernel pointers */' to previous if statement. Also could you add Reported-by mentioned by Florent Revest in the next revision?