From: Pavel Begunkov <asml.silence@gmail.com>
Date: Sat, 9 Jan 2021 16:02:57 +0000 (+0000)
Subject: splice: don't generate zero-len segement bvecs
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=0f1d344feb534555a0dcd0beafb7211a37c5355e;p=linux.git

splice: don't generate zero-len segement bvecs

iter_file_splice_write() may spawn bvec segments with zero-length. In
preparation for prohibiting them, filter out by hand at splice level.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/fs/splice.c b/fs/splice.c
index 866d5c2367b23..474fb8b5562ac 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -662,12 +662,14 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 		/* build the vector */
 		left = sd.total_len;
-		for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++, n++) {
+		for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++) {
 			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
 			size_t this_len = buf->len;
 
-			if (this_len > left)
-				this_len = left;
+			/* zero-length bvecs are not supported, skip them */
+			if (!this_len)
+				continue;
+			this_len = min(this_len, left);
 
 			ret = pipe_buf_confirm(pipe, buf);
 			if (unlikely(ret)) {
@@ -680,6 +682,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 			array[n].bv_len = this_len;
 			array[n].bv_offset = buf->offset;
 			left -= this_len;
+			n++;
 		}
 
 		iov_iter_bvec(&from, WRITE, array, n, sd.total_len - left);