configfs: fix the read and write iterators

Commit 7fe1e79b59ba ("configfs: implement the .read_iter and .write_iter
methods") changed the simple_read_from_buffer() calls into copy_to_iter()
calls and the simple_write_to_buffer() calls into copy_from_iter() calls.
The simple*buffer() methods update the file offset (*ppos) but the read
and write iterators not yet. Make the read and write iterators update the
file offset (iocb->ki_pos).

This patch has been tested as follows:

 # modprobe target_core_user
 # dd if=/sys/kernel/config/target/dbroot bs=1
/var/target
12+0 records in
12+0 records out
12 bytes copied, 9.5539e-05 s, 126 kB/s

 # cd /sys/kernel/config/acpi/table
 # mkdir test
 # cd test
 # dmesg -c >/dev/null; printf 'SSDT\x8\0\0\0abcdefghijklmnopqrstuvwxyz' | dd of=aml bs=1; dmesg -c
34+0 records in
34+0 records out
34 bytes copied, 0.010627 s, 3.2 kB/s
[  261.056551] ACPI configfs: invalid table length

Reported-by: Yanko Kaneti <yaneti@declera.com>
Cc: Yanko Kaneti <yaneti@declera.com>
Fixes: 7fe1e79b59ba ("configfs: implement the .read_iter and .write_iter methods")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/configfs/file.c b/fs/configfs/file.c
index 2f63bf3..5a0be99 100644 (file)
--- a/fs/configfs/file.c
+++ b/fs/configfs/file.c
@@ -91,7 +91,10 @@ static ssize_t configfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
        }
        pr_debug("%s: count = %zd, pos = %lld, buf = %s\n",
                 __func__, iov_iter_count(to), iocb->ki_pos, buffer->page);
-       retval = copy_to_iter(buffer->page, buffer->count, to);
+       if (iocb->ki_pos >= buffer->count)
+               goto out;
+       retval = copy_to_iter(buffer->page + iocb->ki_pos,
+                             buffer->count - iocb->ki_pos, to);
        iocb->ki_pos += retval;
        if (retval == 0)
                retval = -EFAULT;
@@ -162,7 +165,10 @@ static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
                buffer->needs_read_fill = 0;
        }
 
-       retval = copy_to_iter(buffer->bin_buffer, buffer->bin_buffer_size, to);
+       if (iocb->ki_pos >= buffer->bin_buffer_size)
+               goto out;
+       retval = copy_to_iter(buffer->bin_buffer + iocb->ki_pos,
+                             buffer->bin_buffer_size - iocb->ki_pos, to);
        iocb->ki_pos += retval;
        if (retval == 0)
                retval = -EFAULT;
@@ -171,21 +177,28 @@ out:
        return retval;
 }
 
-static int fill_write_buffer(struct configfs_buffer *buffer,
+/* Fill [buffer, buffer + pos) with data coming from @from. */
+static int fill_write_buffer(struct configfs_buffer *buffer, loff_t pos,
                             struct iov_iter *from)
 {
+       loff_t to_copy;
        int copied;
+       u8 *to;
 
        if (!buffer->page)
                buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
        if (!buffer->page)
                return -ENOMEM;
 
-       copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
+       to_copy = SIMPLE_ATTR_SIZE - 1 - pos;
+       if (to_copy <= 0)
+               return 0;
+       to = buffer->page + pos;
+       copied = copy_from_iter(to, to_copy, from);
        buffer->needs_read_fill = 1;
        /* if buf is assumed to contain a string, terminate it by \0,
         * so e.g. sscanf() can scan the string easily */
-       buffer->page[copied] = 0;
+       to[copied] = 0;
        return copied ? : -EFAULT;
 }
 
@@ -217,7 +230,7 @@ static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
        ssize_t len;
 
        mutex_lock(&buffer->mutex);
-       len = fill_write_buffer(buffer, from);
+       len = fill_write_buffer(buffer, iocb->ki_pos, from);
        if (len > 0)
                len = flush_write_buffer(file, buffer, len);
        if (len > 0)
@@ -272,7 +285,9 @@ static ssize_t configfs_bin_write_iter(struct kiocb *iocb,
                buffer->bin_buffer_size = end_offset;
        }
 
-       len = copy_from_iter(buffer->bin_buffer, buffer->bin_buffer_size, from);
+       len = copy_from_iter(buffer->bin_buffer + iocb->ki_pos,
+                            buffer->bin_buffer_size - iocb->ki_pos, from);
+       iocb->ki_pos += len;
 out:
        mutex_unlock(&buffer->mutex);
        return len ? : -EFAULT;