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Wed, 29 Nov 2023 04:51:32 -0800 (PST) Date: Wed, 29 Nov 2023 12:51:08 +0000 In-Reply-To: <20231129-alice-file-v1-0-f81afe8c7261@google.com> Mime-Version: 1.0 References: <20231129-alice-file-v1-0-f81afe8c7261@google.com> X-Developer-Key: i=aliceryhl@google.com; a=openpgp; fpr=49F6C1FAA74960F43A5B86A1EE7A392FDE96209F X-Developer-Signature: v=1; a=openpgp-sha256; l=6667; i=aliceryhl@google.com; h=from:subject:message-id; bh=t47S0WZDVMIoa027rtsW157b15A9bzwhfrZLuzcINm0=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBlZzMy43el8c2O94uLKsnTeu1ybBZWvATM7f0cf BISvhh54g2JAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCZWczMgAKCRAEWL7uWMY5 RufXD/9m/h8mCcP5EbfN4dPSygW7RpJ+QIus6e6EEUo4+to0xhSzDPAN6BNxGP3RpOkle5lLSQH ae5cbBUluG5xEuvmoxRsW7UoaAXDUWQubZBLiuUlKzC+90UHknLFMyYpPNCLEZ/KAFeuMZ9/hSO 71ZhTJHZnge+O6bruAtFShQSQ5izfcldRce9WT7BDHamq54gf5arqb+d3IG5mQE6j5Nb3IargqR G2HMrlczL9/f5SXwLIsi3gGGC8U6EoPjBeoL/IX2SJ6oe9glgqc/8oKvrGdWNGc7of//TNAWyJU kjDZLiD2qymDZMW16Y9/gDvzA8nUYJ8yFucfDSGfl5J8CEbeG/t8MacJCEb4w3M23WzH5KzM/MX SxrXPUwWuuluYfvs76zIQp7VH6yg/zYpRSkcNHceWpDQBt5MneCv5lb/LDJyyUJj47jkC2Ey4Ya xBQIWr7RX7f63nU5D4ajNFQHvCVCpVSk/JJlMMGXR3/jocIUrbhW0eHraEX04qckruzE7wAwxaN kbiPyhThuCiyo9JtnKNoduMG5jyU87sIOM+b9Y7OWVOEeVKpDakGoPjP/84GvXIntuB759JPTxM /1wENIDAxy/KWM+31H70oQ94X6z9bRw7FWnBdevCF/ARG9Jk+KkvIck+nrSwYC1tUtBk9TeG824 sXUo65AMCEvaYHg== X-Mailer: git-send-email 2.43.0.rc1.413.gea7ed67945-goog Message-ID: <20231129-alice-file-v1-2-f81afe8c7261@google.com> Subject: [PATCH 2/7] rust: cred: add Rust abstraction for `struct cred` From: Alice Ryhl To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Benno Lossin , Andreas Hindborg , Peter Zijlstra , Alexander Viro , Christian Brauner , Greg Kroah-Hartman , "=?utf-8?q?Arve_Hj=C3=B8nnev=C3=A5g?=" , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan Cc: Alice Ryhl , Dan Williams , Kees Cook , Matthew Wilcox , Thomas Gleixner , Daniel Xu , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable From: Wedson Almeida Filho Add a wrapper around `struct cred` called `Credential`, and provide functionality to get the `Credential` associated with a `File`. Rust Binder must check the credentials of processes when they attempt to perform various operations, and these checks usually take a `&Credential` as parameter. The security_binder_set_context_mgr function would be one example. This patch is necessary to access these security_* methods from Rust. Signed-off-by: Wedson Almeida Filho Co-developed-by: Alice Ryhl Signed-off-by: Alice Ryhl --- rust/bindings/bindings_helper.h | 1 + rust/helpers.c | 13 +++++++++ rust/kernel/cred.rs | 64 +++++++++++++++++++++++++++++++++++++= ++++ rust/kernel/file.rs | 16 +++++++++++ rust/kernel/lib.rs | 1 + 5 files changed, 95 insertions(+) diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helpe= r.h index beed3ef1fbc3..6d1bd2229aab 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -7,6 +7,7 @@ */ =20 #include +#include #include #include #include diff --git a/rust/helpers.c b/rust/helpers.c index 03141a3608a4..10ed69f76424 100644 --- a/rust/helpers.c +++ b/rust/helpers.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include #include @@ -164,6 +165,18 @@ struct file *rust_helper_get_file(struct file *f) } EXPORT_SYMBOL_GPL(rust_helper_get_file); =20 +const struct cred *rust_helper_get_cred(const struct cred *cred) +{ + return get_cred(cred); +} +EXPORT_SYMBOL_GPL(rust_helper_get_cred); + +void rust_helper_put_cred(const struct cred *cred) +{ + put_cred(cred); +} +EXPORT_SYMBOL_GPL(rust_helper_put_cred); + /* * `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can * use it in contexts where Rust expects a `usize` like slice (array) indi= ces. diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs new file mode 100644 index 000000000000..497058ec89bb --- /dev/null +++ b/rust/kernel/cred.rs @@ -0,0 +1,64 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Credentials management. +//! +//! C header: [`include/linux/cred.h`](../../../../include/linux/cred.h) +//! +//! Reference: + +use crate::{ + bindings, + types::{AlwaysRefCounted, Opaque}, +}; + +/// Wraps the kernel's `struct cred`. +/// +/// # Invariants +/// +/// Instances of this type are always ref-counted, that is, a call to `get= _cred` ensures that the +/// allocation remains valid at least until the matching call to `put_cred= `. +#[repr(transparent)] +pub struct Credential(pub(crate) Opaque); + +// SAFETY: By design, the only way to access a `Credential` is via an immu= table reference or an +// `ARef`. This means that the only situation in which a `Credential` can = be accessed mutably is +// when the refcount drops to zero and the destructor runs. It is safe for= that to happen on any +// thread, so it is ok for this type to be `Send`. +unsafe impl Send for Credential {} + +// SAFETY: It's OK to access `Credential` through shared references from o= ther threads because +// we're either accessing properties that don't change or that are properl= y synchronised by C code. +unsafe impl Sync for Credential {} + +impl Credential { + /// Creates a reference to a [`Credential`] from a valid pointer. + /// + /// # Safety + /// + /// The caller must ensure that `ptr` is valid and remains valid for t= he lifetime of the + /// returned [`Credential`] reference. + pub unsafe fn from_ptr<'a>(ptr: *const bindings::cred) -> &'a Credenti= al { + // SAFETY: The safety requirements guarantee the validity of the d= ereference, while the + // `Credential` type being transparent makes the cast ok. + unsafe { &*ptr.cast() } + } + + /// Returns the effective UID of the given credential. + pub fn euid(&self) -> bindings::kuid_t { + // SAFETY: By the type invariant, we know that `self.0` is valid. + unsafe { (*self.0.get()).euid } + } +} + +// SAFETY: The type invariants guarantee that `Credential` is always ref-c= ounted. +unsafe impl AlwaysRefCounted for Credential { + fn inc_ref(&self) { + // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. + unsafe { bindings::get_cred(self.0.get()) }; + } + + unsafe fn dec_ref(obj: core::ptr::NonNull) { + // SAFETY: The safety requirements guarantee that the refcount is = nonzero. + unsafe { bindings::put_cred(obj.cast().as_ptr()) }; + } +} diff --git a/rust/kernel/file.rs b/rust/kernel/file.rs index ee4ec8b919af..f1f71c3d97e2 100644 --- a/rust/kernel/file.rs +++ b/rust/kernel/file.rs @@ -7,6 +7,7 @@ =20 use crate::{ bindings, + cred::Credential, error::{code::*, Error, Result}, types::{ARef, AlwaysRefCounted, Opaque}, }; @@ -138,6 +139,21 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::file)= -> &'a File { unsafe { &*ptr.cast() } } =20 + /// Returns the credentials of the task that originally opened the fil= e. + pub fn cred(&self) -> &Credential { + // This `read_volatile` is intended to correspond to a READ_ONCE c= all. + // + // SAFETY: The file is valid because the shared reference guarante= es a nonzero refcount. + // + // TODO: Replace with `read_once` when available on the Rust side. + let ptr =3D unsafe { core::ptr::addr_of!((*self.0.get()).f_cred).r= ead_volatile() }; + + // SAFETY: The signature of this function ensures that the caller = will only access the + // returned credential while the file is still valid, and the cred= ential must stay valid + // while the file is valid. + unsafe { Credential::from_ptr(ptr) } + } + /// Returns the flags associated with the file. /// /// The flags are a combination of the constants in [`flags`]. diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index ce9abceab784..097fe9bb93ed 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -33,6 +33,7 @@ #[cfg(not(testlib))] mod allocator; mod build_assert; +pub mod cred; pub mod error; pub mod file; pub mod init; --=20 2.43.0.rc1.413.gea7ed67945-goog