From 851849824bb5590e61048bdd3b311aadeb6a032a Mon Sep 17 00:00:00 2001 From: Wedson Almeida Filho Date: Sun, 15 Sep 2024 14:31:29 +0000 Subject: rust: file: add Rust abstraction for `struct file` This abstraction makes it possible to manipulate the open files for a process. The new `File` struct wraps the C `struct file`. When accessing it using the smart pointer `ARef`, the pointer will own a reference count to the file. When accessing it as `&File`, then the reference does not own a refcount, but the borrow checker will ensure that the reference count does not hit zero while the `&File` is live. Since this is intended to manipulate the open files of a process, we introduce an `fget` constructor that corresponds to the C `fget` method. In future patches, it will become possible to create a new fd in a process and bind it to a `File`. Rust Binder will use these to send fds from one process to another. We also provide a method for accessing the file's flags. Rust Binder will use this to access the flags of the Binder fd to check whether the non-blocking flag is set, which affects what the Binder ioctl does. This introduces a struct for the EBADF error type, rather than just using the Error type directly. This has two advantages: * `File::fget` returns a `Result, BadFdError>`, which the compiler will represent as a single pointer, with null being an error. This is possible because the compiler understands that `BadFdError` has only one possible value, and it also understands that the `ARef` smart pointer is guaranteed non-null. * Additionally, we promise to users of the method that the method can only fail with EBADF, which means that they can rely on this promise without having to inspect its implementation. That said, there are also two disadvantages: * Defining additional error types involves boilerplate. * The question mark operator will only utilize the `From` trait once, which prevents you from using the question mark operator on `BadFdError` in methods that return some third error type that the kernel `Error` is convertible into. (However, it works fine in methods that return `Error`.) Signed-off-by: Wedson Almeida Filho Co-developed-by: Daniel Xu Signed-off-by: Daniel Xu Co-developed-by: Alice Ryhl Reviewed-by: Benno Lossin Signed-off-by: Alice Ryhl Link: https://lore.kernel.org/r/20240915-alice-file-v10-3-88484f7a3dcf@google.com Reviewed-by: Gary Guo Signed-off-by: Christian Brauner --- rust/helpers/helpers.c | 1 + 1 file changed, 1 insertion(+) (limited to 'rust/helpers/helpers.c') diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index 30f40149f3a9..3f2d0d0c8017 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -12,6 +12,7 @@ #include "build_assert.c" #include "build_bug.c" #include "err.c" +#include "fs.c" #include "kunit.c" #include "mutex.c" #include "page.c" -- cgit From a3df991d3d0648dabf761cee70bc1a1ef874db8b Mon Sep 17 00:00:00 2001 From: Wedson Almeida Filho Date: Sun, 15 Sep 2024 14:31:30 +0000 Subject: rust: cred: add Rust abstraction for `struct cred` 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. This Rust abstraction makes the following assumptions about the C side: * `struct cred` is refcounted with `get_cred`/`put_cred`. * It's okay to transfer a `struct cred` across threads, that is, you do not need to call `put_cred` on the same thread as where you called `get_cred`. * The `euid` field of a `struct cred` never changes after initialization. * The `f_cred` field of a `struct file` never changes after initialization. Signed-off-by: Wedson Almeida Filho Co-developed-by: Alice Ryhl Reviewed-by: Trevor Gross Reviewed-by: Benno Lossin Reviewed-by: Martin Rodriguez Reboredo Reviewed-by: Gary Guo Signed-off-by: Alice Ryhl Link: https://lore.kernel.org/r/20240915-alice-file-v10-4-88484f7a3dcf@google.com Reviewed-by: Kees Cook Reviewed-by: Paul Moore Signed-off-by: Christian Brauner --- rust/helpers/helpers.c | 1 + 1 file changed, 1 insertion(+) (limited to 'rust/helpers/helpers.c') diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index 3f2d0d0c8017..16e5de352dab 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -11,6 +11,7 @@ #include "bug.c" #include "build_assert.c" #include "build_bug.c" +#include "cred.c" #include "err.c" #include "fs.c" #include "kunit.c" -- cgit From 94d356c0335f95412575c4fa3954b48722359c8a Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Sun, 15 Sep 2024 14:31:31 +0000 Subject: rust: security: add abstraction for secctx Add an abstraction for viewing the string representation of a security context. This is needed by Rust Binder because it has a feature where a process can view the string representation of the security context for incoming transactions. The process can use that to authenticate incoming transactions, and since the feature is provided by the kernel, the process can trust that the security context is legitimate. This abstraction makes the following assumptions about the C side: * When a call to `security_secid_to_secctx` is successful, it returns a pointer and length. The pointer references a byte string and is valid for reading for that many bytes. * The string may be referenced until `security_release_secctx` is called. * If CONFIG_SECURITY is set, then the three methods mentioned in rust/helpers are available without a helper. (That is, they are not a #define or `static inline`.) Reviewed-by: Benno Lossin Reviewed-by: Martin Rodriguez Reboredo Reviewed-by: Trevor Gross Reviewed-by: Gary Guo Signed-off-by: Alice Ryhl Link: https://lore.kernel.org/r/20240915-alice-file-v10-5-88484f7a3dcf@google.com Acked-by: Paul Moore Reviewed-by: Kees Cook Signed-off-by: Christian Brauner --- rust/helpers/helpers.c | 1 + 1 file changed, 1 insertion(+) (limited to 'rust/helpers/helpers.c') diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index 16e5de352dab..62022b18caf5 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -19,6 +19,7 @@ #include "page.c" #include "rbtree.c" #include "refcount.c" +#include "security.c" #include "signal.c" #include "slab.c" #include "spinlock.c" -- cgit