From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f182.google.com (mail-pf1-f182.google.com [209.85.210.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BCB173FC3 for ; Sun, 22 Aug 2021 14:59:53 +0000 (UTC) Received: by mail-pf1-f182.google.com with SMTP id y190so13131032pfg.7 for ; Sun, 22 Aug 2021 07:59:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=KtofH/4/jYATs6D3O66/kVjkwIShCI9KUHIKJ5lCCCQ=; b=FppxUShmrv1HQlTx8QZBDRPqLPtReo25tMpskXxjbrkbA4X1jxuCaO4f6Jneu1lUsJ IdYXunWAD0daSap4XsBjkgT8GoEdcyeMjXonPXUCMkqLZSMPeXhVWatiGgJuHPEPX8P9 7uxra4LgX1SoqkAwok8hnkAnjgVqNbQocISMg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=KtofH/4/jYATs6D3O66/kVjkwIShCI9KUHIKJ5lCCCQ=; b=learKW+Tn8fzM8TPhjrR2Fy0Lpx79QfcaxatDOzJZ1iqrZl5Qv8OElnpTb9vZmt9xm n+RkjlJcqHAtz/GQEC1k2qmSWIp5FVwdmtdkx6bCvQbzEnbMsPBPMl87jLM9Ugf4hsHG zzpTTdFp+MkhEfY7KE9tvOHNT10A4+Vz7sVsGCymGzsliUzLERvmG1mA1TlFFK3PEHhD Hj+Aqk1nLCBWz2G7KRlE1zeyT3KBl3t/9X5KfTRG9glIbFrDVZX0dnWkj8hLKdudmzoA Fd9pWBIcV0h59wNnP8VHjqEGZpY4+kedrosM7vvWyXHlsQYavwHywDMc5rodZNSAh8+b n+jA== X-Gm-Message-State: AOAM530gxud4ihH6ePPwUCeD0+R10jiwL3trshVAMrx3xV3Q5ByXHlXJ VlnNRhzLbTATEGGtY+s8sPTuqw== X-Google-Smtp-Source: ABdhPJz24gydAFeYUmKy99MGb+xa3/haHNHNvNWd9CFYlv2OtlpJDxbQgxEgWQfqFeiqxwGK01QHjA== X-Received: by 2002:a63:1247:: with SMTP id 7mr27588364pgs.366.1629644393320; Sun, 22 Aug 2021 07:59:53 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id t18sm12779320pfg.111.2021.08.22.07.59.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Aug 2021 07:59:52 -0700 (PDT) Date: Sun, 22 Aug 2021 07:59:51 -0700 From: Kees Cook To: Len Baker Cc: Greg Kroah-Hartman , Michael Straube , Lee Jones , linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 2/2] staging/rtl8192u: Prefer kcalloc over open coded arithmetic Message-ID: <202108220751.4E6ADBA@keescook> References: <20210822142820.5109-1-len.baker@gmx.com> <20210822142820.5109-3-len.baker@gmx.com> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210822142820.5109-3-len.baker@gmx.com> On Sun, Aug 22, 2021 at 04:28:20PM +0200, Len Baker wrote: > Dynamic size calculations (especially multiplication) should not be > performed in memory allocator (or similar) function arguments due to the > risk of them overflowing. This could lead to values wrapping around and > a smaller allocation being made than the caller was expecting. Using > those allocations could lead to linear overflows of heap memory and > other misbehaviors. > > So, use the purpose specific kcalloc() function instead of the argument > size * count in the kzalloc() function. It might be useful to reference the documentation on why this change is desired: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments Here and in the docs, though, it's probably worth noting that these aren't actually dynamic sizes: both sides of the multiplication are constant values. I still think it's best to refactor these anyway, just to keep the open-coded math idiom out of code, though. Also, have you looked at Coccinelle at all? I have a hideous pile of rules that try to find these instances, but it really needs improvement: https://github.com/kees/coccinelle-linux-allocator-overflow/tree/trunk/array_size Reviewed-by: Kees Cook > > Signed-off-by: Len Baker > --- > drivers/staging/rtl8192u/r819xU_phy.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/staging/rtl8192u/r819xU_phy.c b/drivers/staging/rtl8192u/r819xU_phy.c > index ff6fe2ee3349..97f4d89500ae 100644 > --- a/drivers/staging/rtl8192u/r819xU_phy.c > +++ b/drivers/staging/rtl8192u/r819xU_phy.c > @@ -1195,17 +1195,17 @@ static u8 rtl8192_phy_SwChnlStepByStep(struct net_device *dev, u8 channel, > u8 e_rfpath; > bool ret; > > - pre_cmd = kzalloc(sizeof(*pre_cmd) * MAX_PRECMD_CNT, GFP_KERNEL); > + pre_cmd = kcalloc(MAX_PRECMD_CNT, sizeof(*pre_cmd), GFP_KERNEL); > if (!pre_cmd) > return false; > > - post_cmd = kzalloc(sizeof(*post_cmd) * MAX_POSTCMD_CNT, GFP_KERNEL); > + post_cmd = kcalloc(MAX_POSTCMD_CNT, sizeof(*post_cmd), GFP_KERNEL); > if (!post_cmd) { > kfree(pre_cmd); > return false; > } > > - rf_cmd = kzalloc(sizeof(*rf_cmd) * MAX_RFDEPENDCMD_CNT, GFP_KERNEL); > + rf_cmd = kcalloc(MAX_RFDEPENDCMD_CNT, sizeof(*rf_cmd), GFP_KERNEL); > if (!rf_cmd) { > kfree(pre_cmd); > kfree(post_cmd); > -- > 2.25.1 > -- Kees Cook