From: Christian Brauner <christian.brauner@ubuntu.com>
To: Omar Sandoval <osandov@osandov.com>
Cc: linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
Al Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
Dave Chinner <david@fromorbit.com>, Jann Horn <jannh@google.com>,
Amir Goldstein <amir73il@gmail.com>,
Aleksa Sarai <cyphar@cyphar.com>,
linux-api@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH v8 01/10] iov_iter: add copy_struct_from_iter()
Date: Wed, 17 Mar 2021 18:56:11 +0100 [thread overview]
Message-ID: <20210317175611.adntftl6w3avptvk@wittgenstein> (raw)
In-Reply-To: <e71e712d27b2e2c19efc5b1454bd8581ad98d900.1615922644.git.osandov@fb.com>
On Tue, Mar 16, 2021 at 12:42:57PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
>
> This is essentially copy_struct_from_user() but for an iov_iter.
>
> Suggested-by: Aleksa Sarai <cyphar@cyphar.com>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
> include/linux/uio.h | 2 ++
> lib/iov_iter.c | 82 +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 84 insertions(+)
>
> diff --git a/include/linux/uio.h b/include/linux/uio.h
> index 72d88566694e..f4e6ea85a269 100644
> --- a/include/linux/uio.h
> +++ b/include/linux/uio.h
> @@ -121,6 +121,8 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
> struct iov_iter *i);
> size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
> struct iov_iter *i);
> +int copy_struct_from_iter(void *dst, size_t ksize, struct iov_iter *i,
> + size_t usize);
>
> size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
> size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index a21e6a5792c5..f45826ed7528 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -948,6 +948,88 @@ size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
> }
> EXPORT_SYMBOL(copy_page_from_iter);
>
> +/**
> + * copy_struct_from_iter - copy a struct from an iov_iter
> + * @dst: Destination buffer.
> + * @ksize: Size of @dst struct.
> + * @i: Source iterator.
> + * @usize: (Alleged) size of struct in @i.
> + *
> + * Copies a struct from an iov_iter in a way that guarantees
> + * backwards-compatibility for struct arguments in an iovec (as long as the
> + * rules for copy_struct_from_user() are followed).
> + *
> + * The recommended usage is that @usize be taken from the current segment:
> + *
> + * int do_foo(struct iov_iter *i)
> + * {
> + * size_t usize = iov_iter_single_seg_count(i);
> + * struct foo karg;
> + * int err;
> + *
> + * if (usize > PAGE_SIZE)
> + * return -E2BIG;
> + * if (usize < FOO_SIZE_VER0)
> + * return -EINVAL;
> + * err = copy_struct_from_iter(&karg, sizeof(karg), i, usize);
> + * if (err)
> + * return err;
> + *
> + * // ...
> + * }
> + *
> + * Return: 0 on success, -errno on error (see copy_struct_from_user()).
> + *
> + * On success, the iterator is advanced @usize bytes. On error, the iterator is
> + * not advanced.
> + */
> +int copy_struct_from_iter(void *dst, size_t ksize, struct iov_iter *i,
> + size_t usize)
> +{
> + if (usize <= ksize) {
> + if (!copy_from_iter_full(dst, usize, i))
> + return -EFAULT;
> + memset(dst + usize, 0, ksize - usize);
> + } else {
> + size_t copied = 0, copy;
> + int ret;
> +
> + if (WARN_ON(iov_iter_is_pipe(i)) || unlikely(i->count < usize))
> + return -EFAULT;
> + if (iter_is_iovec(i))
> + might_fault();
> + iterate_all_kinds(i, usize, v, ({
> + copy = min(ksize - copied, v.iov_len);
> + if (copy && copyin(dst + copied, v.iov_base, copy))
> + return -EFAULT;
> + copied += copy;
> + ret = check_zeroed_user(v.iov_base + copy,
> + v.iov_len - copy);
> + if (ret <= 0)
> + return ret ?: -E2BIG;
> + 0;}), ({
> + char *addr = kmap_atomic(v.bv_page);
> + copy = min_t(size_t, ksize - copied, v.bv_len);
> + memcpy(dst + copied, addr + v.bv_offset, copy);
> + copied += copy;
> + ret = memchr_inv(addr + v.bv_offset + copy, 0,
> + v.bv_len - copy) ? -E2BIG : 0;
> + kunmap_atomic(addr);
> + if (ret)
> + return ret;
> + }), ({
> + copy = min(ksize - copied, v.iov_len);
> + memcpy(dst + copied, v.iov_base, copy);
> + if (memchr_inv(v.iov_base, 0, v.iov_len))
> + return -E2BIG;
> + })
> + )
Following the semantics of copy_struct_from_user() is certainly a good
idea but can this in any way be rewritten to not look like this; at
least not as crammed. It's a bit painful to follow here what's going.
next prev parent reply other threads:[~2021-03-17 17:57 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 19:42 [PATCH v8 00/10] fs: interface for directly reading/writing compressed data Omar Sandoval
2021-03-16 19:42 ` [PATCH man-pages v8] Document encoded I/O Omar Sandoval
2021-03-16 19:42 ` [PATCH v8 01/10] iov_iter: add copy_struct_from_iter() Omar Sandoval
2021-03-17 17:56 ` Christian Brauner [this message]
2021-03-17 18:45 ` Omar Sandoval
2021-03-20 10:04 ` Christian Brauner
2021-03-16 19:42 ` [PATCH v8 02/10] fs: add O_ALLOW_ENCODED open flag Omar Sandoval
2021-03-16 19:42 ` [PATCH v8 03/10] fs: add RWF_ENCODED for reading/writing compressed data Omar Sandoval
2021-03-16 19:43 ` [PATCH v8 04/10] btrfs: fix check_data_csum() error message for direct I/O Omar Sandoval
2021-03-17 11:21 ` Qu Wenruo
2021-03-17 18:33 ` Omar Sandoval
2021-03-17 23:47 ` Qu Wenruo
2021-03-18 20:25 ` David Sterba
2021-03-16 19:43 ` [PATCH v8 05/10] btrfs: don't advance offset for compressed bios in btrfs_csum_one_bio() Omar Sandoval
2021-03-16 19:43 ` [PATCH v8 06/10] btrfs: add ram_bytes and offset to btrfs_ordered_extent Omar Sandoval
2021-03-16 19:43 ` [PATCH v8 07/10] btrfs: support different disk extent size for delalloc Omar Sandoval
2021-03-16 19:43 ` [PATCH v8 08/10] btrfs: optionally extend i_size in cow_file_range_inline() Omar Sandoval
2021-03-16 19:43 ` [PATCH v8 09/10] btrfs: implement RWF_ENCODED reads Omar Sandoval
2021-03-16 19:43 ` [PATCH v8 10/10] btrfs: implement RWF_ENCODED writes Omar Sandoval
2021-03-19 18:21 ` [PATCH v8 00/10] fs: interface for directly reading/writing compressed data Josef Bacik
2021-03-19 20:08 ` Linus Torvalds
2021-03-19 20:12 ` Josef Bacik
2021-03-19 20:27 ` Omar Sandoval
2021-03-19 20:43 ` Christian Brauner
2021-03-19 20:55 ` Linus Torvalds
2021-03-19 21:11 ` Omar Sandoval
2021-03-19 21:47 ` Linus Torvalds
2021-03-19 22:46 ` Omar Sandoval
2021-03-20 0:31 ` Linus Torvalds
2021-03-20 20:39 ` Omar Sandoval
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