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b=KxEl+0yIHaoC/2sFKknwVY9LXHni1wZ8KvZPSue5iPljBfPw2GOrk5/Ql8LhrrS9E MwrD9Q3ycnCM12f7vxumi3xZw4Zf16PD3R9uUHkwWJfIeonWwbXUpbtxDvZd5cag5h YczD0wjIRbg85aHBwUKAtVlI/cPGiWuJHVWRObnKtJYDg/MaKijBsBgTYapTbGdFrB g7U13so1jTcULm6OTjsv/l5nDwemjGx5md0hlKhWtNf6hp7T5Kqi4BfFh01guvhhwI Nv/Ku5xUfhfZ3H+6lbo6zS7uVNG5zbk8nq12epPSKvYbW9t2bplUaNg3NkxXaA70Kb ZbUsoCX+H+KaA== Received: by cwcc.thunk.org (Postfix, from userid 15806) id E4E6015C013F; Wed, 05 Feb 2025 00:26:51 -0500 (EST) Date: Wed, 5 Feb 2025 00:26:51 -0500 From: "Theodore Ts'o" To: Mateusz Guzik Cc: Kees Cook , syzbot , akpm@linux-foundation.org, brauner@kernel.org, gustavoars@kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [hardening?] [mm?] BUG: bad usercopy in vfs_readlink Message-ID: <20250205052651.GD909029@mit.edu> References: <67a1e1f4.050a0220.163cdc.0063.GAE@google.com> <202502040717.FCEFDB7E0@keescook> <20250204203059.GA909029@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 442461C0009 X-Stat-Signature: 498m68soeztpu3d1r59b94xnrbom7wo3 X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1738733227-115107 X-HE-Meta: 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 sINl6oKp Qwq/tV3qFlv7f9vym87vj+7t6CHpoqTbL7iyrg4raNo4Car5UVQ+za8PK1W8wCek2JkjC48e6N7NgbDh8IPq+MiDs1kRyMNDCiFgfXyxVR1FZnIp/+gkLn1QbDgaX1OoRo7U8Kkj2l3Tby21flxRxtSZQqm5yiknhgPKomn0DaW67yjCdl52dXO1g62co7TOxF8J8xpWM7fKaiyr13tLlnO0rrjEzmdBVNMkDJ6U+aEqDAgpB1yDZZDKyanNmeNeFTNsF8BpT8k1x/m9gYqxEjoPPBWKcdCJuLx4GYMY+Is6YWpqdc9QTbZlOU/4EKE5WY9hKVDD4m1HX4AwH6UpyDGyQQliGl4ONC6no7DgU3e78LrcQxxas88MAgesJqvkazfY+g3v3JqPIPDy6m9tofSAkmA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.002745, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 04, 2025 at 10:25:29PM +0100, Mateusz Guzik wrote: > > > > My question is if that's legitimate, I'm guessing not. If not, then > > ext4 should complain about it. > > > > On stock kernel this happens to work because strlen finds the "right" size. > > > > So it occurred to me to check what fsck thinks about it. > > I ran it twice in a row, it *removed* the problematic symlink. Can you show me what's in the problematic symlink? And does the syzbot reproducer trigger a problem before adding your symlink caching? What would be really great if you couldcreate small focused test case that shows what's going on --- ideally something like a 100k file system, ala the file systems in the tests directory of the e2fsprogs sources.... - Ted