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b=WMjVI9iWkodLGabPriQPIp3DlznF5/DEc9dSKbJM6eEPare7zajZflkO1uG2lePs0 aflrxJllg4kPZ5nNqLlkqP8hWO4W5ThAinZAww478FjUTEIpBi1Ib+eMZFEPV1p9Bq 63p+2qrAZien6ta+ylnKSPyRklWsFXJUDifDcV3eT1OFfG9G1/DN97+6bwUCZTGOKd +14s/5fh/jo8qh/yHPZXsp5RJgNia7Ku9Kkrf87d7rw5cFJDsiIV4nyTJLMSCEsfYd yYyZ4fB1ojIfWyTkIeeAIiLj9fWOd2G0ELy4Ucd3MnS3UsDjE+SMPDNoot2+UAX7iG bwwId3d/VUuTQ== Message-ID: <12d8c91d-d839-4f3d-aca8-0c63e66354d7@kernel.org> Date: Mon, 16 Mar 2026 13:44:36 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: vbabka@kernel.org Subject: Re: [syzbot] [mm?] KMSAN: uninit-value in copy_from_kernel_nofault Content-Language: en-US To: Christian Brauner , syzbot , Alexander Potapenko , Marco Elver , Dmitry Vyukov Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, david@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, mhocko@suse.com, rppt@kernel.org, surenb@google.com, syzkaller-bugs@googlegroups.com, kasan-dev References: <69b7d9f6.050a0220.248e02.0112.GAE@google.com> <20260316-fachtagung-gelitten-17389c00b6c2@brauner> In-Reply-To: <20260316-fachtagung-gelitten-17389c00b6c2@brauner> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 745qti83mq3quzd61fkw641h4atqqsy6 X-Rspamd-Queue-Id: 0929C1C000B X-Rspamd-Server: rspam03 X-HE-Tag: 1773665082-681247 X-HE-Meta: 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 5/F/EXYx gtWlzAsK/oFK54ua0v+hITIyfehWjPE0KuXZz8r7jppLdt3BQuFdk53xxkTwT0j8x6GUv3luJSJGiGQe9qveS8068+PjInzCMy8tNdmUGmXIzMghN+imiXW2y5xBjzmLMRYX1fuLuu3cVpHC4VHyoExfF26WelltODX8bN1IsP6cqzUwSM7oSX8/3EIAjgyb0CEkFjTPkdCcQ8CSYMAv/Pgv7Y4pdPzgapkV2Nh5kZw/J/tEaC93WF6dOyRPPcQV3x9qXnVyaWk1nScHU5fVdQYjm/sGPUpxUE3J08bmHk7xGJ558FTng+uHHkQOdx7f85pDfHlVbqeWRUPTaN/OFXzUXoq4+rG5nAqHGNbFjBFwlNqdvirNFfHyWTquXFbedQbhUAL4z5/A07BI/aXR8IRzeyj0dvR9D+NXfvo4Q7C4yvoQJH8Ziv4oY9UaFX3IzUOZ3gMCUGRmLvc2/pNF0evEK4QpzxwOPhong5gHrWkH+mxpRtTmSWTuD5gVIKab1KVi9Vs7mlOgKR+ZuOWlwb1SM3MhLntNEYOTQZT05cC/TE7WlBvpDyjYPrm+29CVmXHryZt01mC2QAzs+7ESdg998Qs+tF7cj9dnoNpr+9aZY6w7kplWFgVkoL6XHJBxycHPVMY1UnmzeytzPaKk1TOJ3f38FQdfIFkHZVu08aNOjxFLqlb4fYXLr1SC51elOd02Fwskbc0x6rCGntlbxS/Jzq9bNTM9gBZ1o2avw8+yRya+Tyi0i8OyFJML7duzOgY9WEldB7MTNMJOITgwMX69ZxyyMTHOaHCB2Dsc/ZhmeH6nNkcdcAMlSThquW6SQfXud0pbrx3XZRi0HS+j7FkjCB4B0+yKpONiaFvq3tLyUTACQ7fhXdzM6i6fyqJW02SVDS2qS8wo2Rf12PnjyUEJsO+M44ZpgLPS+UqaO07xB+LlfiahPgeFe3nyVhRFEMA88 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/16/26 12:58, Christian Brauner wrote: > On Mon, Mar 16, 2026 at 03:22:46AM -0700, syzbot wrote: >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 80234b5ab240 Merge tag 'rproc-v7.0-fixes' of git://git.ker.. >> git tree: upstream >> console output: https://syzkaller.appspot.com/x/log.txt?x=1474cd52580000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=242f02fcd3fbc8f3 >> dashboard link: https://syzkaller.appspot.com/bug?extid=c18de0ad13d62f18469d >> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 >> userspace arch: i386 >> >> Unfortunately, I don't have any reproducer for this issue yet. >> >> Downloadable assets: >> disk image: https://storage.googleapis.com/syzbot-assets/a0d037332dff/disk-80234b5a.raw.xz >> vmlinux: https://storage.googleapis.com/syzbot-assets/0a1f7f8b54f8/vmlinux-80234b5a.xz >> kernel image: https://storage.googleapis.com/syzbot-assets/83eb68ee6421/bzImage-80234b5a.xz >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+c18de0ad13d62f18469d@syzkaller.appspotmail.com >> >> ===================================================== >> BUG: KMSAN: uninit-value in copy_from_kernel_nofault+0x15f/0x570 mm/maccess.c:41 >> copy_from_kernel_nofault+0x15f/0x570 mm/maccess.c:41 >> prepend_copy fs/d_path.c:50 [inline] >> prepend fs/d_path.c:76 [inline] >> prepend_name fs/d_path.c:101 [inline] >> __prepend_path fs/d_path.c:133 [inline] >> prepend_path+0x64e/0x1090 fs/d_path.c:172 > > I think this might just be KMSAN not being able to deal with seqlocks > appropriately? Let's cc KMSAN folks then. Maybe there's a way to teach it that/add exceptions/ignores. > dentry->d_shortname.string[DNAME_INLINE_LEN-1] = 0; > > is initialized with a zero byte at the end instead of: > > memset(&dentry->d_shortname, 0, sizeof(dentry->d_shortname)); > > which would prevent that warning. But that's zeroing 40 bytes vs one and > the dache is fast-fast-fast. > > prepend_path() detects the initialization race via rename_lock seqlock > and retries d_absolute_path(). So this is entirely harmless and works > correct.