Re: [PATCH v2 4/8] vfs: add missing checks to copy_file_range

Darrick J. Wong
2019-05-28T16:19:24Z

On Sun, May 26, 2019 at 09:10:55AM +0300, Amir Goldstein wrote:
> Like the clone and dedupe interfaces we've recently fixed, the
> copy_file_range() implementation is missing basic sanity, limits and
> boundary condition tests on the parameters that are passed to it
> from userspace. Create a new "generic_copy_file_checks()" function
> modelled on the generic_remap_checks() function to provide this
> missing functionality.
>
> [Amir] Shorten copy length instead of checking pos_in limits
> because input file size already abides by the limits.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
> fs/read_write.c | 3 ++-
> include/linux/fs.h | 3 +++
> mm/filemap.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 58 insertions(+), 1 deletion(-)
>
> diff --git a/fs/read_write.c b/fs/read_write.c
> index f1900bdb3127..b0fb1176b628 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -1626,7 +1626,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> return -EXDEV;
>
> - ret = generic_file_rw_checks(file_in, file_out);
> + ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
> + flags);
> if (unlikely(ret))
> return ret;
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 89b9b73eb581..e4d382c4342a 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3050,6 +3050,9 @@ extern int generic_remap_checks(struct file *file_in, loff_t pos_in,
> struct file *file_out, loff_t pos_out,
> loff_t *count, unsigned int remap_flags);
> extern int generic_file_rw_checks(struct file *file_in, struct file *file_out);
> +extern int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
> + struct file *file_out, loff_t pos_out,
> + size_t *count, unsigned int flags);
> extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
> extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
> extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 798aac92cd76..1852fbf08eeb 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3064,6 +3064,59 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
> return 0;
> }
>
> +/*
> + * Performs necessary checks before doing a file copy
> + *
> + * Can adjust amount of bytes to copy

That's the @req_count parameter, correct?

> + * Returns appropriate error code that caller should return or
> + * zero in case the copy should be allowed.
> + */
> +int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
> + struct file *file_out, loff_t pos_out,
> + size_t *req_count, unsigned int flags)
> +{
> + struct inode *inode_in = file_inode(file_in);
> + struct inode *inode_out = file_inode(file_out);
> + uint64_t count = *req_count;
> + loff_t size_in;
> + int ret;
> +
> + ret = generic_file_rw_checks(file_in, file_out);
> + if (ret)
> + return ret;
> +
> + /* Don't touch certain kinds of inodes */
> + if (IS_IMMUTABLE(inode_out))
> + return -EPERM;
> +
> + if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
> + return -ETXTBSY;
> +
> + /* Ensure offsets don't wrap. */
> + if (pos_in + count < pos_in || pos_out + count < pos_out)
> + return -EOVERFLOW;
> +
> + /* Shorten the copy to EOF */
> + size_in = i_size_read(inode_in);
> + if (pos_in >= size_in)
> + count = 0;
> + else
> + count = min(count, size_in - (uint64_t)pos_in);

Do we need a call to generic_access_check_limits(file_in...) here to
prevent copies from ranges that the page cache doesn't support?

--D

> + ret = generic_write_check_limits(file_out, pos_out, &count);
> + if (ret)
> + return ret;
> +
> + /* Don't allow overlapped copying within the same file. */
> + if (inode_in == inode_out &&
> + pos_out + count > pos_in &&
> + pos_out < pos_in + count)
> + return -EINVAL;
> +
> + *req_count = count;
> + return 0;
> +}
> +
> int pagecache_write_begin(struct file *file, struct address_space *mapping,
> loff_t pos, unsigned len, unsigned flags,
> struct page **pagep, void **fsdata)
> --
> 2.17.1
>