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Date: Tue, 1 Apr 2025 05:17:09 -0700
From: Breno Leitao <leitao@debian.org>
To: Stefan Metzmacher <metze@samba.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Jens Axboe <axboe@kernel.dk>,
Pavel Begunkov <asml.silence@gmail.com>,
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=?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@kernel.org>,
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io-uring@vger.kernel.org
Subject: Re: [RFC PATCH 1/4] net: introduce get_optlen() and put_optlen()
helpers
Message-ID: <Z+vZRcbvh6r1fnZL@gmail.com>
References: <cover.1743449872.git.metze@samba.org>
<156e83128747b2cf7c755bffa68f2519bd255f78.1743449872.git.metze@samba.org>
Precedence: bulk
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In-Reply-To: <156e83128747b2cf7c755bffa68f2519bd255f78.1743449872.git.metze@samba.org>
Hello Stefan,
On Mon, Mar 31, 2025 at 10:10:53PM +0200, Stefan Metzmacher wrote:
> --- a/include/linux/sockptr.h
> +++ b/include/linux/sockptr.h
> @@ -169,4 +169,26 @@ static inline int check_zeroed_sockptr(sockptr_t src, size_t offset,
> return memchr_inv(src.kernel + offset, 0, size) == NULL;
> }
>
> +#define __check_optlen_t(__optlen) \
> +({ \
> + int __user *__ptr __maybe_unused = __optlen; \
> + BUILD_BUG_ON(sizeof(*(__ptr)) != sizeof(int)); \
> +})
I am a bit confused about this macro. I understand that this macro's
goal is to check that __optlen is a pointer to an integer, otherwise
failed to build.
It is unclear to me if that is what it does. Let's suppose that __optlen
is not an integer pointer. Then:
> int __user *__ptr __maybe_unused = __optlen;
This will generate a compile failure/warning due invalid casting,
depending on -Wincompatible-pointer-types.
> BUILD_BUG_ON(sizeof(*(__ptr)) != sizeof(int));
Then this comparison will always false, since __ptr is a pointer to int,
and you are comparing the size of its content with the sizeof(int).