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

On Jul  3, 2026 Alice Ryhl [off-list ref] 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 (local)
---
 rust/kernel/task.rs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Merged into lsm/dev, thanks!

--
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