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    Subject[PATCH 03/11] fs: don't allow splice read/write without explicit ops
    Date
    default_file_splice_write is the last piece of generic code that uses
    set_fs to make the uaccess routines operate on kernel pointers. It
    implements a "fallback loop" for splicing from files that do not actually
    provide a proper splice_read method. The usual file systems and other
    high bandwith instances all provide a ->splice_read, so this just removes
    support for various device drivers and procfs/debugfs files. If splice
    support for any of those turns out to be important it can be added back
    by switching them to the iter ops and using generic_file_splice_read.

    Signed-off-by: Christoph Hellwig <hch@lst.de>
    ---
    fs/read_write.c | 2 +-
    fs/splice.c | 130 +++++----------------------------------------
    include/linux/fs.h | 2 -
    3 files changed, 15 insertions(+), 119 deletions(-)

    diff --git a/fs/read_write.c b/fs/read_write.c
    index 702c4301d9eb6b..8c61f67453e3d3 100644
    --- a/fs/read_write.c
    +++ b/fs/read_write.c
    @@ -1077,7 +1077,7 @@ ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
    }
    EXPORT_SYMBOL(vfs_iter_write);

    -ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
    +static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
    unsigned long vlen, loff_t *pos, rwf_t flags)
    {
    struct iovec iovstack[UIO_FASTIOV];
    diff --git a/fs/splice.c b/fs/splice.c
    index d7c8a7c4db07ff..412df7b48f9eb7 100644
    --- a/fs/splice.c
    +++ b/fs/splice.c
    @@ -342,89 +342,6 @@ const struct pipe_buf_operations nosteal_pipe_buf_ops = {
    };
    EXPORT_SYMBOL(nosteal_pipe_buf_ops);

    -static ssize_t kernel_readv(struct file *file, const struct kvec *vec,
    - unsigned long vlen, loff_t offset)
    -{
    - mm_segment_t old_fs;
    - loff_t pos = offset;
    - ssize_t res;
    -
    - old_fs = get_fs();
    - set_fs(KERNEL_DS);
    - /* The cast to a user pointer is valid due to the set_fs() */
    - res = vfs_readv(file, (const struct iovec __user *)vec, vlen, &pos, 0);
    - set_fs(old_fs);
    -
    - return res;
    -}
    -
    -static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
    - struct pipe_inode_info *pipe, size_t len,
    - unsigned int flags)
    -{
    - struct kvec *vec, __vec[PIPE_DEF_BUFFERS];
    - struct iov_iter to;
    - struct page **pages;
    - unsigned int nr_pages;
    - unsigned int mask;
    - size_t offset, base, copied = 0;
    - ssize_t res;
    - int i;
    -
    - if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
    - return -EAGAIN;
    -
    - /*
    - * Try to keep page boundaries matching to source pagecache ones -
    - * it probably won't be much help, but...
    - */
    - offset = *ppos & ~PAGE_MASK;
    -
    - iov_iter_pipe(&to, READ, pipe, len + offset);
    -
    - res = iov_iter_get_pages_alloc(&to, &pages, len + offset, &base);
    - if (res <= 0)
    - return -ENOMEM;
    -
    - nr_pages = DIV_ROUND_UP(res + base, PAGE_SIZE);
    -
    - vec = __vec;
    - if (nr_pages > PIPE_DEF_BUFFERS) {
    - vec = kmalloc_array(nr_pages, sizeof(struct kvec), GFP_KERNEL);
    - if (unlikely(!vec)) {
    - res = -ENOMEM;
    - goto out;
    - }
    - }
    -
    - mask = pipe->ring_size - 1;
    - pipe->bufs[to.head & mask].offset = offset;
    - pipe->bufs[to.head & mask].len -= offset;
    -
    - for (i = 0; i < nr_pages; i++) {
    - size_t this_len = min_t(size_t, len, PAGE_SIZE - offset);
    - vec[i].iov_base = page_address(pages[i]) + offset;
    - vec[i].iov_len = this_len;
    - len -= this_len;
    - offset = 0;
    - }
    -
    - res = kernel_readv(in, vec, nr_pages, *ppos);
    - if (res > 0) {
    - copied = res;
    - *ppos += res;
    - }
    -
    - if (vec != __vec)
    - kfree(vec);
    -out:
    - for (i = 0; i < nr_pages; i++)
    - put_page(pages[i]);
    - kvfree(pages);
    - iov_iter_advance(&to, copied); /* truncates and discards */
    - return res;
    -}
    -
    /*
    * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
    * using sendpage(). Return the number of bytes sent.
    @@ -788,33 +705,6 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,

    EXPORT_SYMBOL(iter_file_splice_write);

    -static int write_pipe_buf(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
    - struct splice_desc *sd)
    -{
    - int ret;
    - void *data;
    - loff_t tmp = sd->pos;
    -
    - data = kmap(buf->page);
    - ret = __kernel_write(sd->u.file, data + buf->offset, sd->len, &tmp);
    - kunmap(buf->page);
    -
    - return ret;
    -}
    -
    -static ssize_t default_file_splice_write(struct pipe_inode_info *pipe,
    - struct file *out, loff_t *ppos,
    - size_t len, unsigned int flags)
    -{
    - ssize_t ret;
    -
    - ret = splice_from_pipe(pipe, out, ppos, len, flags, write_pipe_buf);
    - if (ret > 0)
    - *ppos += ret;
    -
    - return ret;
    -}
    -
    /**
    * generic_splice_sendpage - splice data from a pipe to a socket
    * @pipe: pipe to splice from
    @@ -836,15 +726,23 @@ ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,

    EXPORT_SYMBOL(generic_splice_sendpage);

    +static int warn_unsupported(struct file *file, const char *op)
    +{
    + pr_debug_ratelimited(
    + "splice %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
    + op, file, current->pid, current->comm);
    + return -EINVAL;
    +}
    +
    /*
    * Attempt to initiate a splice from pipe to file.
    */
    static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
    loff_t *ppos, size_t len, unsigned int flags)
    {
    - if (out->f_op->splice_write)
    - return out->f_op->splice_write(pipe, out, ppos, len, flags);
    - return default_file_splice_write(pipe, out, ppos, len, flags);
    + if (unlikely(!out->f_op->splice_write))
    + return warn_unsupported(out, "write");
    + return out->f_op->splice_write(pipe, out, ppos, len, flags);
    }

    /*
    @@ -866,9 +764,9 @@ static long do_splice_to(struct file *in, loff_t *ppos,
    if (unlikely(len > MAX_RW_COUNT))
    len = MAX_RW_COUNT;

    - if (in->f_op->splice_read)
    - return in->f_op->splice_read(in, ppos, pipe, len, flags);
    - return default_file_splice_read(in, ppos, pipe, len, flags);
    + if (unlikely(!in->f_op->splice_read))
    + return warn_unsupported(in, "read");
    + return in->f_op->splice_read(in, ppos, pipe, len, flags);
    }

    /**
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index e019ea2f1347e6..d33cc3e8ed410b 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1894,8 +1894,6 @@ ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,

    extern ssize_t vfs_read(struct file *, char __user *, size_t, loff_t *);
    extern ssize_t vfs_write(struct file *, const char __user *, size_t, loff_t *);
    -extern ssize_t vfs_readv(struct file *, const struct iovec __user *,
    - unsigned long, loff_t *, rwf_t);
    extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file *,
    loff_t, size_t, unsigned int);
    extern ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
    --
    2.28.0
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