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Sat, 23 May 2026 13:41:38 -0700 (PDT) From: Askar Safin To: brauner@kernel.org Cc: axboe@kernel.dk, jack@suse.cz, jannh@google.com, kees@kernel.org, linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mjguzik@gmail.com, pfalcato@suse.de, viro@zeniv.linux.org.uk, David Howells Subject: Re: [RFC PATCH] fs/splice: allow for a way to block splice() with read-only files Date: Sat, 23 May 2026 23:41:00 +0300 Message-ID: <20260523204100.553125-1-safinaskar@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <177918418452.771415.4371785688744608623.b4-reply@b4> References: <177918418452.771415.4371785688744608623.b4-reply@b4> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Christian Brauner : > Let's discuss the other aggressive alternative: Can we try and > unconditionally degrade to copy. This would affect sendfile(), splice(), > and vmsplice(). Worst-case we would have to introduce the sysctl > retroactively. > > Thoughts? I think as a first step we should make vmsplice unconditionally equivalent to readv/writev. vmsplice already was problematic from security point of view long time ago. I mean CVE-2020-29374 (see https://lwn.net/Articles/849638/ ). David Howells also doesn't like vmsplice: https://lore.kernel.org/all/1763225.1769180226@warthog.procyon.org.uk/ Linus said in 2023: > So I'd personally be perfectly ok with just making vmsplice() be > exactly the same as write, and turn all of vmsplice() into just "it's > a read() if the pipe is open for read, and a write if it's open for > writing". https://lore.kernel.org/all/CAHk-=wgG_2cmHgZwKjydi7=iimyHyN8aessnbM9XQ9ufbaUz9g@mail.gmail.com/ Even experts get vmsplice wrong, as can be seen in this thread: https://lore.kernel.org/all/CAAUqJDvFuvms55Td1c=XKv6epfRnnP78438nZQ-JKyuCptGBiQ@mail.gmail.com/T/#u As you can see in that thread, it is very hard to understand what vmsplice man page supposed to mean. And you can also see that vmsplice is very fragile. -- Askar Safin