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AHgh+RpdFaPkbIjV2BBgckZybVjrZtC/NdtUf5lrpVvFchZ9e2/cdUnbfo+f3fwSUCbff4mH9Zl/ygRtPOwlmHX0vg==@vger.kernel.org X-Gm-Message-State: AOJu0YwNMirM43xqw7Uvnn7kIijbIO/fUMkZYOTvbSFb+ThQCH8E5qHo qMZSApdawm8cxMqUQSjnrQniwlIGIdGzVN/g4Y7TD0ZtmrzluKpWssLWjhPD9WcP9ZNJ41oOtSJ +nHfA9hT3Mp7voPsqRQ== X-Received: from wmjl19.prod.google.com ([2002:a7b:c353:0:b0:493:bdba:620b]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:34d6:b0:493:aa0a:45b0 with SMTP id 5b1f17b1804b1-493df08f925mr889185e9.23.1783338919855; Mon, 06 Jul 2026 04:55:19 -0700 (PDT) Date: Mon, 6 Jul 2026 11:55:18 +0000 In-Reply-To: <20260613065348.96750-5-work@onurozkan.dev> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260613065348.96750-1-work@onurozkan.dev> <20260613065348.96750-5-work@onurozkan.dev> Message-ID: Subject: Re: [PATCH v10 4/5] rust: sync: add SRCU abstraction From: Alice Ryhl To: "Onur =?utf-8?B?w5Z6a2Fu?=" , boqun@kernel.org Cc: rcu@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, ojeda@kernel.org, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, tmgross@umich.edu, dakr@kernel.org, peterz@infradead.org, fujita.tomonori@gmail.com, tamird@kernel.org, jiangshanlai@gmail.com, paulmck@kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Sat, Jun 13, 2026 at 09:40:10AM +0300, Onur =C3=96zkan wrote: > +#[pinned_drop] > +impl PinnedDrop for Srcu { > + fn drop(self: Pin<&mut Self>) { > + let ptr =3D self.inner.get(); > + > + if crate::warn_on!( > + // SAFETY: By the type invariants, `self` contains a valid a= nd pinned `struct srcu_struct` > + // and `srcu_readers_active()` only checks the active reader= count. > + unsafe { bindings::srcu_readers_active(ptr) } > + ) { > + // `cleanup_srcu_struct()` may return early if there are sti= ll active readers. > + // This should only happen if a guard was leaked with `mem::= forget`, which is > + // "WRONG" code and may cause a UAF because Rust will free t= he `srcu_struct` > + // while it is still referenced from the C side (e.g. by `ca= ll_srcu()` callbacks). > + // > + // Another consequence of leaking guards is that `call_srcu(= )` callbacks will > + // never run because the grace period can never complete due= to permanently > + // active readers (i.e. leaked guards). > + // > + // If this ever happens, that means the guard was leaked by = mistake and the > + // caller must fix the bug. Sleeping here is intentional and= less harmful > + // than risking a UAF. > + // > + // SAFETY: By the type invariants, `self` contains a valid a= nd pinned > + // `struct srcu_struct`. > + unsafe { bindings::synchronize_srcu(ptr) }; > + } > + > + // Ensure all SRCU callbacks have been finished before freeing. > + // SAFETY: By the type invariants, `self` contains a valid and p= inned `struct srcu_struct`. > + unsafe { bindings::srcu_barrier(ptr) }; Hmm. It's not entirely clear to me that synchronize_srcu() is needed here. If there are calls to srcu_read_lock() that do not have a matching unlock due to use of mem::forget(), then either there is a pending call_srcu() callback in the queue, in which case srcu_barrier() already sleeps forever, or there are no such callbacks in which case I don't think this actually leads to UAF. Thoughts? Alice