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Wed, 18 Aug 2021 01:12:15 -0700 (PDT) Subject: Re: [syzbot] KFENCE: use-after-free in kvm_fastop_exception To: Matthieu Baerts , syzbot , davem@davemloft.net, johan.hedberg@gmail.com, kuba@kernel.org, linux-bluetooth@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, luiz.dentz@gmail.com, marcel@holtmann.org, mathew.j.martineau@linux.intel.com, netdev@vger.kernel.org, pabeni@redhat.com, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk References: <00000000000012030e05c9c8bc85@google.com> <58cef9e0-69de-efdb-4035-7c1ed3d23132@tessares.net> From: Pavel Skripkin Message-ID: <6736a510-20a1-9fb5-caf4-86334cabbbb6@gmail.com> Date: Wed, 18 Aug 2021 11:12:14 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <58cef9e0-69de-efdb-4035-7c1ed3d23132@tessares.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/18/21 11:02 AM, Matthieu Baerts wrote: > Hello, > > On 18/08/2021 00:21, syzbot wrote: >> syzbot has bisected this issue to: >> >> commit c4512c63b1193c73b3f09c598a6d0a7f88da1dd8 >> Author: Matthieu Baerts >> Date: Fri Jun 25 21:25:22 2021 +0000 >> >> mptcp: fix 'masking a bool' warning >> >> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=122b0655300000 >> start commit: b9011c7e671d Add linux-next specific files for 20210816 >> git tree: linux-next >> final oops: https://syzkaller.appspot.com/x/report.txt?x=112b0655300000 >> console output: https://syzkaller.appspot.com/x/log.txt?x=162b0655300000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=a245d1aa4f055cc1 >> dashboard link: https://syzkaller.appspot.com/bug?extid=7b938780d5deeaaf938f >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=157a41ee300000 >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14f78ff9300000 > > I'm pretty sure the commit c4512c63b119 ("mptcp: fix 'masking a bool' > warning") doesn't introduce the reported bug. This minor fix is specific > to MPTCP which doesn't seem to be used here. > > I'm not sure how I can tell syzbot this is a false positive. > looks like it's fs/namei bug. Similar reports: https://syzkaller.appspot.com/bug?id=517fa734b92b7db404c409b924cf5c997640e324 https://syzkaller.appspot.com/bug?id=484483daf3652b40dae18531923aa9175d392a4d It's not false positive. I've suggested the fix here: https://groups.google.com/g/syzkaller-bugs/c/HE3c2fP5nic/m/1Yk17GBeAwAJ I am waiting for author comments about the fix :) But, yes, syzbot bisection is often wrong, so don't rely on it much :) With regards, Pavel Skripkin