| Message ID | 20240915-alice-file-v10-7-88484f7a3dcf@google.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | File abstractions needed by Rust Binder | expand |
On Sun, 15 Sep 2024 14:31:33 +0000 Alice Ryhl <aliceryhl@google.com> wrote: > Adds a wrapper around `kuid_t` called `Kuid`. This allows us to define > various operations on kuids such as equality and current_euid. It also > lets us provide conversions from kuid into userspace values. > > Rust Binder needs these operations because it needs to compare kuids for > equality, and it needs to tell userspace about the pid and uid of > incoming transactions. > > To read kuids from a `struct task_struct`, you must currently use > various #defines that perform the appropriate field access under an RCU > read lock. Currently, we do not have a Rust wrapper for rcu_read_lock, > which means that for this patch, there are two ways forward: > > 1. Inline the methods into Rust code, and use __rcu_read_lock directly > rather than the rcu_read_lock wrapper. This gives up lockdep for > these usages of RCU. > > 2. Wrap the various #defines in helpers and call the helpers from Rust. > > This patch uses the second option. One possible disadvantage of the > second option is the possible introduction of speculation gadgets, but > as discussed in [1], the risk appears to be acceptable. > > Of course, once a wrapper for rcu_read_lock is available, it is > preferable to use that over either of the two above approaches. > > Link: https://lore.kernel.org/all/202312080947.674CD2DC7@keescook/ [1] > Reviewed-by: Benno Lossin <benno.lossin@proton.me> > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> > Reviewed-by: Trevor Gross <tmgross@umich.edu> > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > rust/bindings/bindings_helper.h | 1 + > rust/helpers/task.c | 38 ++++++++++++++++++++++++ > rust/kernel/cred.rs | 5 ++-- > rust/kernel/task.rs | 66 +++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 108 insertions(+), 2 deletions(-) > > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h > index 51ec78c355c0..e854ccddecee 100644 > --- a/rust/bindings/bindings_helper.h > +++ b/rust/bindings/bindings_helper.h > @@ -19,6 +19,7 @@ > #include <linux/jiffies.h> > #include <linux/mdio.h> > #include <linux/phy.h> > +#include <linux/pid_namespace.h> > #include <linux/refcount.h> > #include <linux/sched.h> > #include <linux/security.h> > diff --git a/rust/helpers/task.c b/rust/helpers/task.c > index 7ac789232d11..7d66487db831 100644 > --- a/rust/helpers/task.c > +++ b/rust/helpers/task.c > @@ -17,3 +17,41 @@ void rust_helper_put_task_struct(struct task_struct *t) > { > put_task_struct(t); > } > + > +kuid_t rust_helper_task_uid(struct task_struct *task) > +{ > + return task_uid(task); > +} > + > +kuid_t rust_helper_task_euid(struct task_struct *task) > +{ > + return task_euid(task); > +} > + > +#ifndef CONFIG_USER_NS > +uid_t rust_helper_from_kuid(struct user_namespace *to, kuid_t uid) > +{ > + return from_kuid(to, uid); > +} > +#endif /* CONFIG_USER_NS */ nit: it's fine to omit this `ifndef`, see what we do for `errname`. > + > +bool rust_helper_uid_eq(kuid_t left, kuid_t right) > +{ > + return uid_eq(left, right); > +} > + > +kuid_t rust_helper_current_euid(void) > +{ > + return current_euid(); > +} > + > +struct user_namespace *rust_helper_current_user_ns(void) > +{ > + return current_user_ns(); > +} > + > +pid_t rust_helper_task_tgid_nr_ns(struct task_struct *tsk, > + struct pid_namespace *ns) > +{ > + return task_tgid_nr_ns(tsk, ns); > +} > diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs > index 367b4bbddd9f..1a36a9f19368 100644 > --- a/rust/kernel/task.rs > +++ b/rust/kernel/task.rs > @@ -9,6 +9,7 @@ > types::{NotThreadSafe, Opaque}, > }; > use core::{ > + cmp::{Eq, PartialEq}, > ffi::{c_int, c_long, c_uint}, > ops::Deref, > ptr, > @@ -96,6 +97,12 @@ unsafe impl Sync for Task {} > /// The type of process identifiers (PIDs). > type Pid = bindings::pid_t; > > +/// The type of user identifiers (UIDs). > +#[derive(Copy, Clone)] > +pub struct Kuid { > + kuid: bindings::kuid_t, > +} > + > impl Task { > /// Returns a raw pointer to the current task. > /// > @@ -157,12 +164,31 @@ pub fn pid(&self) -> Pid { > unsafe { *ptr::addr_of!((*self.0.get()).pid) } > } > > + /// Returns the UID of the given task. > + pub fn uid(&self) -> Kuid { > + // SAFETY: By the type invariant, we know that `self.0` is valid. > + Kuid::from_raw(unsafe { bindings::task_uid(self.0.get()) }) > + } > + > + /// Returns the effective UID of the given task. > + pub fn euid(&self) -> Kuid { > + // SAFETY: By the type invariant, we know that `self.0` is valid. > + Kuid::from_raw(unsafe { bindings::task_euid(self.0.get()) }) > + } > + > /// Determines whether the given task has pending signals. > pub fn signal_pending(&self) -> bool { > // SAFETY: By the type invariant, we know that `self.0` is valid. > unsafe { bindings::signal_pending(self.0.get()) != 0 } > } > > + /// Returns the given task's pid in the current pid namespace. > + pub fn pid_in_current_ns(&self) -> Pid { > + // SAFETY: We know that `self.0.get()` is valid by the type invariant, and passing a null > + // pointer as the namespace is correct for using the current namespace. > + unsafe { bindings::task_tgid_nr_ns(self.0.get(), ptr::null_mut()) } Do we want to rely on the behaviour of `task_tgid_nr_ns` with null pointer as namespace, or use `task_tgid_vnr`? Best, Gary > + } > + > /// Wakes up the task. > pub fn wake_up(&self) { > // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid.
On Mon, Sep 16, 2024 at 12:02 AM Gary Guo <gary@garyguo.net> wrote: > > On Sun, 15 Sep 2024 14:31:33 +0000 > Alice Ryhl <aliceryhl@google.com> wrote: > > + /// Returns the given task's pid in the current pid namespace. > > + pub fn pid_in_current_ns(&self) -> Pid { > > + // SAFETY: We know that `self.0.get()` is valid by the type invariant, and passing a null > > + // pointer as the namespace is correct for using the current namespace. > > + unsafe { bindings::task_tgid_nr_ns(self.0.get(), ptr::null_mut()) } > > Do we want to rely on the behaviour of `task_tgid_nr_ns` with null > pointer as namespace, or use `task_tgid_vnr`? Hmm. Looks like C Binder actually does: trd->sender_pid = task_tgid_nr_ns(sender, task_active_pid_ns(current)); Not sure why I'm using a null pointer here. Alice
On Mon, Sep 23, 2024 at 11:13:56AM GMT, Alice Ryhl wrote: > On Mon, Sep 16, 2024 at 12:02 AM Gary Guo <gary@garyguo.net> wrote: > > > > On Sun, 15 Sep 2024 14:31:33 +0000 > > Alice Ryhl <aliceryhl@google.com> wrote: > > > + /// Returns the given task's pid in the current pid namespace. > > > + pub fn pid_in_current_ns(&self) -> Pid { > > > + // SAFETY: We know that `self.0.get()` is valid by the type invariant, and passing a null > > > + // pointer as the namespace is correct for using the current namespace. > > > + unsafe { bindings::task_tgid_nr_ns(self.0.get(), ptr::null_mut()) } > > > > Do we want to rely on the behaviour of `task_tgid_nr_ns` with null > > pointer as namespace, or use `task_tgid_vnr`? > > Hmm. Looks like C Binder actually does: > trd->sender_pid = task_tgid_nr_ns(sender, task_active_pid_ns(current)); > > Not sure why I'm using a null pointer here. Passing a NULL pointer for task_tgid_nr_ns() is fine. Under the hood it's just __task_pid_nr_ns(task, PIDTYPE_TGID, NULL) which causes task_active_pid_ns(current) to be called internally. So it's equivalent. In any case, I did add Rust wrappers for struct pid_namespace just to see how far I would get as task_active_pid_ns() is rather subtle even if it isn't obvious at first glance. Sending that in a second.
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 51ec78c355c0..e854ccddecee 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -19,6 +19,7 @@ #include <linux/jiffies.h> #include <linux/mdio.h> #include <linux/phy.h> +#include <linux/pid_namespace.h> #include <linux/refcount.h> #include <linux/sched.h> #include <linux/security.h> diff --git a/rust/helpers/task.c b/rust/helpers/task.c index 7ac789232d11..7d66487db831 100644 --- a/rust/helpers/task.c +++ b/rust/helpers/task.c @@ -17,3 +17,41 @@ void rust_helper_put_task_struct(struct task_struct *t) { put_task_struct(t); } + +kuid_t rust_helper_task_uid(struct task_struct *task) +{ + return task_uid(task); +} + +kuid_t rust_helper_task_euid(struct task_struct *task) +{ + return task_euid(task); +} + +#ifndef CONFIG_USER_NS +uid_t rust_helper_from_kuid(struct user_namespace *to, kuid_t uid) +{ + return from_kuid(to, uid); +} +#endif /* CONFIG_USER_NS */ + +bool rust_helper_uid_eq(kuid_t left, kuid_t right) +{ + return uid_eq(left, right); +} + +kuid_t rust_helper_current_euid(void) +{ + return current_euid(); +} + +struct user_namespace *rust_helper_current_user_ns(void) +{ + return current_user_ns(); +} + +pid_t rust_helper_task_tgid_nr_ns(struct task_struct *tsk, + struct pid_namespace *ns) +{ + return task_tgid_nr_ns(tsk, ns); +} diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs index 92659649e932..81d67789b16f 100644 --- a/rust/kernel/cred.rs +++ b/rust/kernel/cred.rs @@ -10,6 +10,7 @@ use crate::{ bindings, + task::Kuid, types::{AlwaysRefCounted, Opaque}, }; @@ -61,11 +62,11 @@ pub fn get_secid(&self) -> u32 { } /// Returns the effective UID of the given credential. - pub fn euid(&self) -> bindings::kuid_t { + pub fn euid(&self) -> Kuid { // SAFETY: By the type invariant, we know that `self.0` is valid. Furthermore, the `euid` // field of a credential is never changed after initialization, so there is no potential // for data races. - unsafe { (*self.0.get()).euid } + Kuid::from_raw(unsafe { (*self.0.get()).euid }) } } diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index 367b4bbddd9f..1a36a9f19368 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -9,6 +9,7 @@ types::{NotThreadSafe, Opaque}, }; use core::{ + cmp::{Eq, PartialEq}, ffi::{c_int, c_long, c_uint}, ops::Deref, ptr, @@ -96,6 +97,12 @@ unsafe impl Sync for Task {} /// The type of process identifiers (PIDs). type Pid = bindings::pid_t; +/// The type of user identifiers (UIDs). +#[derive(Copy, Clone)] +pub struct Kuid { + kuid: bindings::kuid_t, +} + impl Task { /// Returns a raw pointer to the current task. /// @@ -157,12 +164,31 @@ pub fn pid(&self) -> Pid { unsafe { *ptr::addr_of!((*self.0.get()).pid) } } + /// Returns the UID of the given task. + pub fn uid(&self) -> Kuid { + // SAFETY: By the type invariant, we know that `self.0` is valid. + Kuid::from_raw(unsafe { bindings::task_uid(self.0.get()) }) + } + + /// Returns the effective UID of the given task. + pub fn euid(&self) -> Kuid { + // SAFETY: By the type invariant, we know that `self.0` is valid. + Kuid::from_raw(unsafe { bindings::task_euid(self.0.get()) }) + } + /// Determines whether the given task has pending signals. pub fn signal_pending(&self) -> bool { // SAFETY: By the type invariant, we know that `self.0` is valid. unsafe { bindings::signal_pending(self.0.get()) != 0 } } + /// Returns the given task's pid in the current pid namespace. + pub fn pid_in_current_ns(&self) -> Pid { + // SAFETY: We know that `self.0.get()` is valid by the type invariant, and passing a null + // pointer as the namespace is correct for using the current namespace. + unsafe { bindings::task_tgid_nr_ns(self.0.get(), ptr::null_mut()) } + } + /// Wakes up the task. pub fn wake_up(&self) { // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid. @@ -184,3 +210,43 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) { unsafe { bindings::put_task_struct(obj.cast().as_ptr()) } } } + +impl Kuid { + /// Get the current euid. + #[inline] + pub fn current_euid() -> Kuid { + // SAFETY: Just an FFI call. + Self::from_raw(unsafe { bindings::current_euid() }) + } + + /// Create a `Kuid` given the raw C type. + #[inline] + pub fn from_raw(kuid: bindings::kuid_t) -> Self { + Self { kuid } + } + + /// Turn this kuid into the raw C type. + #[inline] + pub fn into_raw(self) -> bindings::kuid_t { + self.kuid + } + + /// Converts this kernel UID into a userspace UID. + /// + /// Uses the namespace of the current task. + #[inline] + pub fn into_uid_in_current_ns(self) -> bindings::uid_t { + // SAFETY: Just an FFI call. + unsafe { bindings::from_kuid(bindings::current_user_ns(), self.kuid) } + } +} + +impl PartialEq for Kuid { + #[inline] + fn eq(&self, other: &Kuid) -> bool { + // SAFETY: Just an FFI call. + unsafe { bindings::uid_eq(self.kuid, other.kuid) } + } +} + +impl Eq for Kuid {}
Adds a wrapper around `kuid_t` called `Kuid`. This allows us to define various operations on kuids such as equality and current_euid. It also lets us provide conversions from kuid into userspace values. Rust Binder needs these operations because it needs to compare kuids for equality, and it needs to tell userspace about the pid and uid of incoming transactions. To read kuids from a `struct task_struct`, you must currently use various #defines that perform the appropriate field access under an RCU read lock. Currently, we do not have a Rust wrapper for rcu_read_lock, which means that for this patch, there are two ways forward: 1. Inline the methods into Rust code, and use __rcu_read_lock directly rather than the rcu_read_lock wrapper. This gives up lockdep for these usages of RCU. 2. Wrap the various #defines in helpers and call the helpers from Rust. This patch uses the second option. One possible disadvantage of the second option is the possible introduction of speculation gadgets, but as discussed in [1], the risk appears to be acceptable. Of course, once a wrapper for rcu_read_lock is available, it is preferable to use that over either of the two above approaches. Link: https://lore.kernel.org/all/202312080947.674CD2DC7@keescook/ [1] Reviewed-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> Reviewed-by: Trevor Gross <tmgross@umich.edu> Signed-off-by: Alice Ryhl <aliceryhl@google.com> --- rust/bindings/bindings_helper.h | 1 + rust/helpers/task.c | 38 ++++++++++++++++++++++++ rust/kernel/cred.rs | 5 ++-- rust/kernel/task.rs | 66 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 108 insertions(+), 2 deletions(-)