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[209.85.219.180]) by smtp.gmail.com with ESMTPSA id c140sm4662643ywa.74.2018.11.14.15.32.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Nov 2018 15:32:22 -0800 (PST) Received: by mail-yb1-f180.google.com with SMTP id w17-v6so7639093ybl.6 for ; Wed, 14 Nov 2018 15:32:22 -0800 (PST) X-Received: by 2002:a25:ac8e:: with SMTP id x14-v6mr3897359ybi.141.1542238341792; Wed, 14 Nov 2018 15:32:21 -0800 (PST) MIME-Version: 1.0 Received: by 2002:a25:b906:0:0:0:0:0 with HTTP; Wed, 14 Nov 2018 15:32:21 -0800 (PST) In-Reply-To: <1542156686-12253-1-git-send-email-isaacm@codeaurora.org> References: <1542156686-12253-1-git-send-email-isaacm@codeaurora.org> From: Kees Cook Date: Wed, 14 Nov 2018 17:32:21 -0600 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check To: "Isaac J. Manjarres" Cc: Chris von Recklinghausen , Linux-MM , LKML , Sodagudi Prasad , tsoni@codeaurora.org, "# 3.4.x" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 13, 2018 at 6:51 PM, Isaac J. Manjarres wrote: > Currently, when checking to see if accessing n bytes starting at > address "ptr" will cause a wraparound in the memory addresses, > the check in check_bogus_address() adds an extra byte, which is > incorrect, as the range of addresses that will be accessed is > [ptr, ptr + (n - 1)]. > > This can lead to incorrectly detecting a wraparound in the > memory address, when trying to read 4 KB from memory that is > mapped to the the last possible page in the virtual address > space, when in fact, accessing that range of memory would not > cause a wraparound to occur. I'm kind of surprised anything is using the -4K memory range -- this is ERR_PTR() area and I'd expect there to be an explicit unallocated memory hole here. > > Use the memory range that will actually be accessed when > considering if accessing a certain amount of bytes will cause > the memory address to wrap around. > > Change-Id: I2563a5988e41122727ede17180f365e999b953e6 > Fixes: f5509cc18daa ("mm: Hardened usercopy") > Co-Developed-by: Prasad Sodagudi > Signed-off-by: Prasad Sodagudi > Signed-off-by: Isaac J. Manjarres > Cc: stable@vger.kernel.org Regardless, I'll take it in my tree if akpm doesn't grab it first. :) Acked-by: Kees Cook -Kees > --- > mm/usercopy.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/usercopy.c b/mm/usercopy.c > index 852eb4e..0293645 100644 > --- a/mm/usercopy.c > +++ b/mm/usercopy.c > @@ -151,7 +151,7 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n, > bool to_user) > { > /* Reject if object wraps past end of memory. */ > - if (ptr + n < ptr) > + if (ptr + (n - 1) < ptr) > usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n); > > /* Reject if NULL or ZERO-allocation. */ > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project > -- Kees Cook