From 17614445576b6af24e9cf36607c6448164719c96 Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Fri, 30 Nov 2018 10:37:49 -0800 Subject: [PATCH] splice: don't read more than available pipe space In commit 4721a601099, we tried to fix a problem wherein directio reads into a splice pipe will bounce EFAULT/EAGAIN all the way out to userspace by simulating a zero-byte short read. This happens because some directio read implementations (xfs) will call bio_iov_iter_get_pages to grab pipe buffer pages and issue asynchronous reads, but as soon as we run out of pipe buffers that _get_pages call returns EFAULT, which the splice code translates to EAGAIN and bounces out to userspace. In that commit, the iomap code catches the EFAULT and simulates a zero-byte read, but that causes assertion errors on regular splice reads because xfs doesn't allow short directio reads. The brokenness is compounded by splice_direct_to_actor immediately bailing on do_splice_to returning <= 0 without ever calling ->actor (which empties out the pipe), so if userspace calls back we'll EFAULT again on the full pipe, and nothing ever gets copied. Therefore, teach splice_direct_to_actor to clamp its requests to the amount of free space in the pipe and remove the simulated short read from the iomap directio code. Fixes: 4721a601099 ("iomap: dio data corruption and spurious errors when pipes fill") Reported-by: Murphy Zhou Ranted-by: Amir Goldstein Reviewed-by: Christoph Hellwig Signed-off-by: Darrick J. Wong --- fs/splice.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/splice.c b/fs/splice.c index 3553f1956508..de2ede048473 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -945,11 +945,16 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd, sd->flags &= ~SPLICE_F_NONBLOCK; more = sd->flags & SPLICE_F_MORE; + WARN_ON_ONCE(pipe->nrbufs != 0); + while (len) { size_t read_len; loff_t pos = sd->pos, prev_pos = pos; - ret = do_splice_to(in, &pos, pipe, len, flags); + /* Don't try to read more the pipe has space for. */ + read_len = min_t(size_t, len, + (pipe->buffers - pipe->nrbufs) << PAGE_SHIFT); + ret = do_splice_to(in, &pos, pipe, read_len, flags); if (unlikely(ret <= 0)) goto out_release;