From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 97ABC27AC41; Tue, 6 May 2025 12:52:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746535962; cv=none; b=V63SwthajCqfz6MfkxEqT8n1Y6+0dzELcwMioshiSyoODAE4DpRMPzdTSI2RZaCdamh2RCPz2GCMfZlplJYUCfpxlJWNa9udcgWKJ6DiJuGK8oSGImlgNQhS4TWex6AevaH0RLPnJiIz7fLBjMTXkQ0GHPvxObe9S7pAmOVBtwA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746535962; c=relaxed/simple; bh=CoGj5SFcRaCss+CpurOaTAPuqA7YnJFs78eMCJRv7H8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aDtYAXpKrDlQ/wcZ8Zg0jaQ8mlB6oPYtIfKmrIELa1nPzPlYtgKYEbwVb5AmlpyhakgE5VkaXTC7QuvtUOcLT/KU/CbOztjTlq80A73MUPypMFEwil9nE4XMs/BCSCklBcLgDpea3damHGDxqjyMILiKkDRZ3z/55FBLPI1M3lk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=gaYu+12Y; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="gaYu+12Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3AABAC4CEE4; Tue, 6 May 2025 12:52:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1746535962; bh=CoGj5SFcRaCss+CpurOaTAPuqA7YnJFs78eMCJRv7H8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gaYu+12YUu9M8YmpGzc0XxsT+IKB0ZKv5u0NT+X9pcZbWFnzcmw/SkQic+ogKcLxD qtyed+o+FA94SdC/r6RXdcse9KifRcdHmsQ/YABoTYXv/E7VnjgPuHoD37ZIpOQ191 yiElZUmotKu6yJIlSsiv+O99p6Vj/yErO8pN3be0= Date: Tue, 6 May 2025 14:52:39 +0200 From: Greg Kroah-Hartman To: Alice Ryhl Cc: Miguel Ojeda , Andrew Morton , Alexander Viro , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] uaccess: rust: add strncpy_from_user Message-ID: <2025050645-trifocals-olympics-4692@gregkh> References: <20250505-strncpy-from-user-v3-0-85c677fd4f91@google.com> <20250505-strncpy-from-user-v3-1-85c677fd4f91@google.com> <2025050544-sneak-compactor-d701@gregkh> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, May 06, 2025 at 09:18:41AM +0000, Alice Ryhl wrote: > On Mon, May 05, 2025 at 04:30:05PM +0200, Greg Kroah-Hartman wrote: > > On Mon, May 05, 2025 at 12:17:31PM +0000, Alice Ryhl wrote: > > > 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..a7b123915e9aa2329f376d67cad93e2fc17ae017 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) -> Result { > > > Ok(()) > > > } > > > } > > > + > > > +/// Reads a nul-terminated string into `buf` and returns the length. > > > +/// > > > +/// This reads from userspace until a NUL byte is encountered, or until `buf.len()` bytes have been > > > +/// read. Fails with [`EFAULT`] if a read happens on a bad address (some data may have been > > > +/// copied). When the end of the buffer is encountered, no NUL byte is added, 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]) -> Result { > > > > Nit, the parameters here are backwards from the C version of > > strncpy_from_user(), which is going to cause us no end of grief when > > reviewing code between the two languages :( > > I'll swap them. > > fn raw_strncpy_from_user(dst: &mut [MaybeUninit], src: UserPtr) -> Result { > > > Also, it's not your fault, but we don't have any type of __user tag for > > data coming from userspace yet to track this type of thing? The > > compiler (well sparse) can catch this type of thing in C, any hints on > > what we could do in Rust for the same type of guarantee (i.e. don't > > touch user data before it's been copied, and then we need to treat it as > > "unverified" but that's a different patch series...) > > The UserPtr typedef is intended to do that, but since it's only a > typedef to usize, the compiler won't detect it if you mix up a user > pointer with a length. (It will detect mix-ups with pointers since we > use an integer type for UserPtr.) Sorry, I missed the "UserPtr" for some reason. But having an integer type for UserPtr feels like it's going to cause problems in the long-run. > What we can do is replace the typedef with > > #[repr(transparent)] > struct UserPtr(pub usize); > > That way, it becomes it's own separate type (this is called the newtype > pattern [1]) so that it can't be mixed up with anything else. Why not use a real pointer like: struct UserPtr(pub *const u8) > The #[repr(transparent)] annotation makes the compiler treat it like a > bare long for ABI-purposes. I'm not sure if any function ABIs actually > treat a long differently from a struct that just contains a long, but if > such ABIs exist, then the annotation ensures that the long ABI is used > rather than the struct-containing-long ABI. In the kernel, "unsigned long" is guaranteed to hold a pointer. Which is why many of the old allocation functions return that type. thanks, greg k-h