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charset="utf-8" Content-Transfer-Encoding: quoted-printable This patch adds a direct wrapper around the C function of the same name. It's not really intended for direct use by Rust code since strncpy_from_user has a somewhat unfortunate API where it only nul-terminates the buffer if there's space for the nul-terminator. This means that a direct Rust wrapper around it could not return a &CStr since the buffer may not be a cstring. However, we still add the method to build more convenient APIs on top of it, which will happen in subsequent patches. Reviewed-by: Danilo Krummrich Reviewed-by: Greg Kroah-Hartman Reviewed-by: Boqun Feng Signed-off-by: Alice Ryhl --- rust/kernel/uaccess.rs | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs index 80a9782b1c6e98ed6eae308ade8551afa7adc188..a7b123915e9aa2329f376d67cad= 93e2fc17ae017 100644 --- a/rust/kernel/uaccess.rs +++ b/rust/kernel/uaccess.rs @@ -8,7 +8,7 @@ alloc::{Allocator, Flags}, bindings, error::Result, - ffi::c_void, + ffi::{c_char, c_void}, prelude::*, transmute::{AsBytes, FromBytes}, }; @@ -369,3 +369,36 @@ pub fn write(&mut self, value: &T) -> Resu= lt { Ok(()) } } + +/// Reads a nul-terminated string into `buf` and returns the length. +/// +/// This reads from userspace until a NUL byte is encountered, or until `b= uf.len()` bytes have been +/// read. Fails with [`EFAULT`] if a read happens on a bad address (some d= ata may have been +/// copied). When the end of the buffer is encountered, no NUL byte is add= ed, so the string is +/// *not* guaranteed to be NUL-terminated when `Ok(buf.len())` is returned. +/// +/// # Guarantees +/// +/// When this function returns `Ok(len)`, it is guaranteed that the first = `len` of `buf` bytes are +/// initialized and non-zero. Furthermore, if `len < buf.len()`, then `buf= [len]` is a NUL byte. +/// Unsafe code may rely on these guarantees. +#[inline] +#[expect(dead_code)] +fn raw_strncpy_from_user(ptr: UserPtr, buf: &mut [MaybeUninit]) -> Res= ult { + // CAST: Slice lengths are guaranteed to be `<=3D isize::MAX`. + let len =3D buf.len() as isize; + + // SAFETY: `buf` is valid for writing `buf.len()` bytes. + let res =3D unsafe { + bindings::strncpy_from_user(buf.as_mut_ptr().cast::(), ptr= as *const c_char, len) + }; + + if res < 0 { + return Err(Error::from_errno(res as i32)); + } + + #[cfg(CONFIG_RUST_OVERFLOW_CHECKS)] + assert!(res <=3D len); + + Ok(res as usize) +} --=20 2.49.0.967.g6a0df3ecc3-goog