Re: [PATCH v5 1/2] rust: task: clarify comments on task UID accessors

[Paul Moore <paul@paul-moore.com>]

On Jul  3, 2026 Alice Ryhl <aliceryhl@google.com> wrote:
> 
> Linux has separate subjective and objective task credentials, see the
> comment above `struct cred`. Clarify which accessor functions operate on
> which set of credentials.
> 
> Also document that Task::euid() is a very weird operation. You can see how
> weird it is by grepping for task_euid() in the history - binder was its
> only user. Task::euid() obtains the objective effective UID - it looks
> at the credentials of the task for purposes of acting on it as an
> object, but then accesses the effective UID (which the credentials.7 man
> page describes as "[...] used by the kernel to determine the permissions
> that the process will have when accessing shared resources [...]").
> 
> For context:
> Arguably, binder's use of task_euid() is a theoretical security problem,
> which only has no impact on Android because Android has no setuid binaries
> executable by apps.
> commit 29bc22ac5e5b ("binder: use euid from cred instead of using task")
> originally fixed that by removing that only user of task_euid(), but the
> fix got reverted in commit c21a80ca0684 ("binder: fix test regression
> due to sender_euid change") because some Android test started failing.
> It was since fixed again by commit 65b672152289 ("binder: use
> current_euid() for transaction sender identity"), which uses
> current_euid() instead.
> 
> Signed-off-by: Jann Horn <jannh@google.com>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> Originally sent as:
> https://lore.kernel.org/r/20260212-rust-uid-v1-1-deff4214c766@google.com
> ---
>  rust/kernel/task.rs | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Merged into lsm/dev, thanks!

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