[PATCH 02/11] fs: don't allow kernel reads and writes without iter ops

Christoph Hellwig
2020-08-17T07:33:39Z

Don't allow calling ->read or ->write with set_fs as a preparation for
killing off set_fs. All the instances that we use kernel_read/write on
are using the iter ops already.

If a file has both the regular ->read/->write methods and the iter
variants those could have different semantics for messed up enough
drivers. Also fails the kernel access to them in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/read_write.c | 67 +++++++++++++++++++++++++++++++------------------
1 file changed, 42 insertions(+), 25 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 5db58b8c78d0dd..702c4301d9eb6b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -419,27 +419,41 @@ static ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, lo
return ret;
}

+static int warn_unsupported(struct file *file, const char *op)
+{
+ pr_warn_ratelimited(
+ "kernel %s not supported for file %pD4 (pid: %d comm: %.20s)\n",
+ op, file, current->pid, current->comm);
+ return -EINVAL;
+}
+
ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
{
- mm_segment_t old_fs = get_fs();
+ struct kvec iov = {
+ .iov_base = buf,
+ .iov_len = min_t(size_t, count, MAX_RW_COUNT),
+ };
+ struct kiocb kiocb;
+ struct iov_iter iter;
ssize_t ret;

if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))
return -EINVAL;
if (!(file->f_mode & FMODE_CAN_READ))
return -EINVAL;
+ /*
+ * Also fail if ->read_iter and ->read are both wired up as that
+ * implies very convoluted semantics.
+ */
+ if (unlikely(!file->f_op->read_iter || file->f_op->read))
+ return warn_unsupported(file, "read");

- if (count > MAX_RW_COUNT)
- count = MAX_RW_COUNT;
- set_fs(KERNEL_DS);
- if (file->f_op->read)
- ret = file->f_op->read(file, (void __user *)buf, count, pos);
- else if (file->f_op->read_iter)
- ret = new_sync_read(file, (void __user *)buf, count, pos);
- else
- ret = -EINVAL;
- set_fs(old_fs);
+ init_sync_kiocb(&kiocb, file);
+ kiocb.ki_pos = *pos;
+ iov_iter_kvec(&iter, READ, &iov, 1, iov.iov_len);
+ ret = file->f_op->read_iter(&kiocb, &iter);
if (ret > 0) {
+ *pos = kiocb.ki_pos;
fsnotify_access(file);
add_rchar(current, ret);
}
@@ -510,28 +524,31 @@ static ssize_t new_sync_write(struct file *filp, const char __user *buf, size_t
/* caller is responsible for file_start_write/file_end_write */
ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos)
{
- mm_segment_t old_fs;
- const char __user *p;
+ struct kvec iov = {
+ .iov_base = (void *)buf,
+ .iov_len = min_t(size_t, count, MAX_RW_COUNT),
+ };
+ struct kiocb kiocb;
+ struct iov_iter iter;
ssize_t ret;

if (WARN_ON_ONCE(!(file->f_mode & FMODE_WRITE)))
return -EBADF;
if (!(file->f_mode & FMODE_CAN_WRITE))
return -EINVAL;
+ /*
+ * Also fail if ->write_iter and ->write are both wired up as that
+ * implies very convoluted semantics.
+ */
+ if (unlikely(!file->f_op->write_iter || file->f_op->write))
+ return warn_unsupported(file, "write");

- old_fs = get_fs();
- set_fs(KERNEL_DS);
- p = (__force const char __user *)buf;
- if (count > MAX_RW_COUNT)
- count = MAX_RW_COUNT;
- if (file->f_op->write)
- ret = file->f_op->write(file, p, count, pos);
- else if (file->f_op->write_iter)
- ret = new_sync_write(file, p, count, pos);
- else
- ret = -EINVAL;
- set_fs(old_fs);
+ init_sync_kiocb(&kiocb, file);
+ kiocb.ki_pos = *pos;
+ iov_iter_kvec(&iter, WRITE, &iov, 1, iov.iov_len);
+ ret = file->f_op->write_iter(&kiocb, &iter);
if (ret > 0) {
+ *pos = kiocb.ki_pos;
fsnotify_modify(file);
add_wchar(current, ret);
}
--
2.28.0