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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id a1sm72180032pgh.61.2019.08.10.11.23.19 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 10 Aug 2019 11:23:19 -0700 (PDT) Date: Sat, 10 Aug 2019 11:23:18 -0700 From: Kees Cook To: Alan Stern Cc: Greg KH , syzbot , Michael Hund , akpm@linux-foundation.org, andreyknvl@google.com, cai@lca.pw, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com, tglx@linutronix.de Subject: Re: BUG: bad usercopy in ld_usb_read Message-ID: <201908101120.BE5034521A@keescook> References: <20190809085545.GB21320@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Aug 09, 2019 at 11:13:00AM -0400, Alan Stern wrote: > In fact, I don't see why any of the computations here should overflow > or wrap around, or even give rise to a negative value. If syzbot had a > reproducer we could get more debugging output -- but it doesn't. Yeah, this is odd. The only thing I could see here with more study was that ring_tail is used/updated outside of the rbsl lock in ld_usb_read(). I couldn't convince myself there wasn't a race against the interrupt, but I also couldn't think of a way it could break... -- Kees Cook