[PATCH v2 05/16] splice: remove permission hook from iter_file_splice_write()

[Amir Goldstein <amir73il@xxxxxxxxx>]

All the callers of ->splice_write(), (e.g. do_splice_direct() and
do_splice()) already check rw_verify_area() for the entire range
and perform all the other checks that are in vfs_write_iter().

Create a helper do_iter_writev(), that performs the write without the
checks and use it in iter_file_splice_write() to avoid the redundant
rw_verify_area() checks.

This is needed for fanotify "pre content" events.

Suggested-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 fs/internal.h   |  8 +++++++-
 fs/read_write.c | 11 +++++++++++
 fs/splice.c     |  9 ++++++---
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 58e43341aebf..c114b85e27a7 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -298,7 +298,13 @@ static inline ssize_t do_get_acl(struct mnt_idmap *idmap,
 }
 #endif
 
-ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos);
+/*
+ * fs/read_write.c
+ */
+ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from,
+			    loff_t *pos);
+ssize_t do_iter_writev(struct file *file, struct iov_iter *iter, loff_t *ppos,
+		       rwf_t flags);
 
 /*
  * fs/attr.c
diff --git a/fs/read_write.c b/fs/read_write.c
index 4771701c896b..313f7eaaa9a7 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -739,6 +739,17 @@ static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
 	return ret;
 }
 
+/*
+ * Low-level helpers don't perform rw sanity checks.
+ * The caller is responsible for that.
+ */
+ssize_t do_iter_writev(struct file *filp, struct iov_iter *iter, loff_t *ppos,
+		       rwf_t flags)
+{
+	return do_iter_readv_writev(filp, iter, ppos, WRITE, flags);
+}
+
+
 /* Do it by hand, with file-ops */
 static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
 		loff_t *ppos, int type, rwf_t flags)
diff --git a/fs/splice.c b/fs/splice.c
index d4fdd44c0b32..decbace5d812 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -673,10 +673,13 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 		.u.file = out,
 	};
 	int nbufs = pipe->max_usage;
-	struct bio_vec *array = kcalloc(nbufs, sizeof(struct bio_vec),
-					GFP_KERNEL);
+	struct bio_vec *array;
 	ssize_t ret;
 
+	if (!out->f_op->write_iter)
+		return -EINVAL;
+
+	array = kcalloc(nbufs, sizeof(struct bio_vec), GFP_KERNEL);
 	if (unlikely(!array))
 		return -ENOMEM;
 
@@ -733,7 +736,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 		}
 
 		iov_iter_bvec(&from, ITER_SOURCE, array, n, sd.total_len - left);
-		ret = vfs_iter_write(out, &from, &sd.pos, 0);
+		ret = do_iter_writev(out, &from, &sd.pos, 0);
 		if (ret <= 0)
 			break;
 
-- 
2.34.1