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[209.6.156.57]) by smtp.gmail.com with ESMTPSA id i14sm2984009qkl.105.2020.05.25.12.50.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 25 May 2020 12:50:48 -0700 (PDT) Subject: Re: [PATCH] staging: vchiq_arm: cast with __force as needed To: Dan Carpenter Cc: Nicolas Saenz Julienne , Greg Kroah-Hartman , Jamal Shareef , Marcelo Diop-Gonzalez , Nishka Dasgupta , devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org References: <20200519004531.33158-1-tasman@leaflabs.com> <20200522110623.GL30374@kadam> From: Mitchell Tasman Message-ID: <4dcf963f-ce9a-fa2b-09c9-c8657f407167@leaflabs.com> Date: Mon, 25 May 2020 15:50:46 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200522110623.GL30374@kadam> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/22/20 7:06 AM, Dan Carpenter wrote: > On Mon, May 18, 2020 at 08:45:31PM -0400, Mitchell Tasman wrote: >> In several cases where a pointer marked as __user is >> (intentionally) assigned or passed to a non-marked target, >> cast to the target pointer type with a __force directive >> to quiet warnings from sparse. >> >> Signed-off-by: Mitchell Tasman >> --- >> .../vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 7 ++++--- >> .../staging/vc04_services/interface/vchiq_arm/vchiq_arm.c | 4 +++- >> 2 files changed, 7 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c >> index c18c6ca0b6c0..38a13e4618a8 100644 >> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c >> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c >> @@ -371,14 +371,15 @@ create_pagelist(char __user *buf, size_t count, unsigned short type) >> pagelistinfo->scatterlist = scatterlist; >> pagelistinfo->scatterlist_mapped = 0; >> >> - if (is_vmalloc_addr(buf)) { >> + if (is_vmalloc_addr((void __force *)buf)) { > > Am I reading this correctly??? > > This is actually a user controlled pointer that comes from the > vchiq_ioctl() when we do VCHIQ_IOC_QUEUE_BULK_TRANSMIT/RECEIVE. So we > take random pointer from user space and if it happens to point to kernel > space then we trust it and presumably start BULK_TRANSMITing data to > it??? > > LOL.... This doesn't seem safe at all. Is additional validation of buf and its extent necessary and sufficient, e.g. perhaps access_ok(buf, count * PAGE_SIZE) somewhere along the call chain? Or does vhciq_arm need to take a different approach in the area that Dan Carpenter flagged? Thank you. > > regards, > dan carpenter > Regards, Mitch