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Subject: [RFC PATCH 05/10] pipe: Allow pipes to have kernel-reserved slots
 [ver #2]
From:   David Howells <dhowells@redhat.com>
To:     torvalds@linux-foundation.org
Cc:     dhowells@redhat.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        nicolas.dichtel@6wind.com, raven@themaw.net,
        Christian Brauner <christian@brauner.io>, dhowells@redhat.com,
        keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-block@vger.kernel.org, linux-security-module@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 23 Oct 2019 21:17:50 +0100
Message-ID: <157186187074.3995.5299010277211516015.stgit@warthog.procyon.org.uk>
In-Reply-To: <157186182463.3995.13922458878706311997.stgit@warthog.procyon.org.uk>
References: <157186182463.3995.13922458878706311997.stgit@warthog.procyon.org.uk>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Split pipe->ring_size into two numbers:

 (1) pipe->ring_size - indicates the hard size of the pipe ring.

 (2) pipe->max_usage - indicates the maximum number of pipe ring slots that
     userspace orchestrated events can fill.

This allows for a pipe that is both writable by the general kernel
notification facility and by userspace, allowing plenty of ring space for
notifications to be added whilst preventing userspace from being able to
pin too much unswappable kernel space.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/fuse/dev.c             |    8 ++++----
 fs/pipe.c                 |   10 ++++++----
 fs/splice.c               |   26 +++++++++++++-------------
 include/linux/pipe_fs_i.h |    6 +++++-
 lib/iov_iter.c            |    4 ++--
 5 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1e4bc27573cc..5ef57a322cb8 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -703,7 +703,7 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
 =09=09=09cs->pipebufs++;
 =09=09=09cs->nr_segs--;
 =09=09} else {
-=09=09=09if (cs->nr_segs >=3D cs->pipe->ring_size)
+=09=09=09if (cs->nr_segs >=3D cs->pipe->max_usage)
 =09=09=09=09return -EIO;
=20
 =09=09=09page =3D alloc_page(GFP_HIGHUSER);
@@ -879,7 +879,7 @@ static int fuse_ref_page(struct fuse_copy_state *cs, st=
ruct page *page,
 =09struct pipe_buffer *buf;
 =09int err;
=20
-=09if (cs->nr_segs >=3D cs->pipe->ring_size)
+=09if (cs->nr_segs >=3D cs->pipe->max_usage)
 =09=09return -EIO;
=20
 =09err =3D unlock_request(cs->req);
@@ -1341,7 +1341,7 @@ static ssize_t fuse_dev_splice_read(struct file *in, =
loff_t *ppos,
 =09if (!fud)
 =09=09return -EPERM;
=20
-=09bufs =3D kvmalloc_array(pipe->ring_size, sizeof(struct pipe_buffer),
+=09bufs =3D kvmalloc_array(pipe->max_usage, sizeof(struct pipe_buffer),
 =09=09=09      GFP_KERNEL);
 =09if (!bufs)
 =09=09return -ENOMEM;
@@ -1353,7 +1353,7 @@ static ssize_t fuse_dev_splice_read(struct file *in, =
loff_t *ppos,
 =09if (ret < 0)
 =09=09goto out;
=20
-=09if (pipe_occupancy(pipe->head, pipe->tail) + cs.nr_segs > pipe->ring_si=
ze) {
+=09if (pipe_occupancy(pipe->head, pipe->tail) + cs.nr_segs > pipe->max_usa=
ge) {
 =09=09ret =3D -EIO;
 =09=09goto out;
 =09}
diff --git a/fs/pipe.c b/fs/pipe.c
index 8a0806fe12d3..12e47cae9425 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -403,7 +403,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
=20
 =09tail =3D pipe->tail;
 =09head =3D pipe->head;
-=09max_usage =3D pipe->ring_size;
+=09max_usage =3D pipe->max_usage;
 =09mask =3D pipe->ring_size - 1;
=20
 =09/* We try to merge small writes */
@@ -570,7 +570,7 @@ pipe_poll(struct file *filp, poll_table *wait)
 =09}
=20
 =09if (filp->f_mode & FMODE_WRITE) {
-=09=09if (!pipe_full(head, tail, pipe->ring_size))
+=09=09if (!pipe_full(head, tail, pipe->max_usage))
 =09=09=09mask |=3D EPOLLOUT | EPOLLWRNORM;
 =09=09/*
 =09=09 * Most Unices do not set EPOLLERR for FIFOs but on Linux they
@@ -695,6 +695,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
 =09if (pipe->bufs) {
 =09=09init_waitqueue_head(&pipe->wait);
 =09=09pipe->r_counter =3D pipe->w_counter =3D 1;
+=09=09pipe->max_usage =3D pipe_bufs;
 =09=09pipe->ring_size =3D pipe_bufs;
 =09=09pipe->user =3D user;
 =09=09mutex_init(&pipe->mutex);
@@ -1149,9 +1150,10 @@ static long pipe_set_size(struct pipe_inode_info *pi=
pe, unsigned long arg)
 =09kfree(pipe->bufs);
 =09pipe->bufs =3D bufs;
 =09pipe->ring_size =3D nr_slots;
+=09pipe->max_usage =3D nr_slots;
 =09pipe->tail =3D tail;
 =09pipe->head =3D head;
-=09return pipe->ring_size * PAGE_SIZE;
+=09return pipe->max_usage * PAGE_SIZE;
=20
 out_revert_acct:
 =09(void) account_pipe_buffers(pipe->user, nr_slots, pipe->ring_size);
@@ -1184,7 +1186,7 @@ long pipe_fcntl(struct file *file, unsigned int cmd, =
unsigned long arg)
 =09=09ret =3D pipe_set_size(pipe, arg);
 =09=09break;
 =09case F_GETPIPE_SZ:
-=09=09ret =3D pipe->ring_size * PAGE_SIZE;
+=09=09ret =3D pipe->max_usage * PAGE_SIZE;
 =09=09break;
 =09default:
 =09=09ret =3D -EINVAL;
diff --git a/fs/splice.c b/fs/splice.c
index bbc025236ff9..03b96eae084b 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -199,7 +199,7 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
 =09=09goto out;
 =09}
=20
-=09while (!pipe_full(head, tail, pipe->ring_size)) {
+=09while (!pipe_full(head, tail, pipe->max_usage)) {
 =09=09struct pipe_buffer *buf =3D &pipe->bufs[head & mask];
=20
 =09=09buf->page =3D spd->pages[page_nr];
@@ -239,7 +239,7 @@ ssize_t add_to_pipe(struct pipe_inode_info *pipe, struc=
t pipe_buffer *buf)
 =09if (unlikely(!pipe->readers)) {
 =09=09send_sig(SIGPIPE, current, 0);
 =09=09ret =3D -EPIPE;
-=09} else if (pipe_full(head, tail, pipe->ring_size)) {
+=09} else if (pipe_full(head, tail, pipe->max_usage)) {
 =09=09ret =3D -EAGAIN;
 =09} else {
 =09=09pipe->bufs[head & mask] =3D *buf;
@@ -257,7 +257,7 @@ EXPORT_SYMBOL(add_to_pipe);
  */
 int splice_grow_spd(const struct pipe_inode_info *pipe, struct splice_pipe=
_desc *spd)
 {
-=09unsigned int max_usage =3D READ_ONCE(pipe->ring_size);
+=09unsigned int max_usage =3D READ_ONCE(pipe->max_usage);
=20
 =09spd->nr_pages_max =3D max_usage;
 =09if (max_usage <=3D PIPE_DEF_BUFFERS)
@@ -381,7 +381,7 @@ static ssize_t default_file_splice_read(struct file *in=
, loff_t *ppos,
 =09ssize_t res;
 =09int i;
=20
-=09if (pipe_full(pipe->head, pipe->tail, pipe->ring_size))
+=09if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
 =09=09return -EAGAIN;
=20
 =09/*
@@ -698,7 +698,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, st=
ruct file *out,
 =09=09.pos =3D *ppos,
 =09=09.u.file =3D out,
 =09};
-=09int nbufs =3D pipe->ring_size;
+=09int nbufs =3D pipe->max_usage;
 =09struct bio_vec *array =3D kcalloc(nbufs, sizeof(struct bio_vec),
 =09=09=09=09=09GFP_KERNEL);
 =09ssize_t ret;
@@ -721,9 +721,9 @@ iter_file_splice_write(struct pipe_inode_info *pipe, st=
ruct file *out,
 =09=09if (ret <=3D 0)
 =09=09=09break;
=20
-=09=09if (unlikely(nbufs < pipe->ring_size)) {
+=09=09if (unlikely(nbufs < pipe->max_usage)) {
 =09=09=09kfree(array);
-=09=09=09nbufs =3D pipe->ring_size;
+=09=09=09nbufs =3D pipe->max_usage;
 =09=09=09array =3D kcalloc(nbufs, sizeof(struct bio_vec),
 =09=09=09=09=09GFP_KERNEL);
 =09=09=09if (!array) {
@@ -963,7 +963,7 @@ ssize_t splice_direct_to_actor(struct file *in, struct =
splice_desc *sd,
 =09=09loff_t pos =3D sd->pos, prev_pos =3D pos;
=20
 =09=09/* Don't try to read more the pipe has space for. */
-=09=09p_space =3D pipe->ring_size -
+=09=09p_space =3D pipe->max_usage -
 =09=09=09pipe_occupancy(pipe->head, pipe->tail);
 =09=09read_len =3D min_t(size_t, len, p_space << PAGE_SHIFT);
 =09=09ret =3D do_splice_to(in, &pos, pipe, read_len, flags);
@@ -1090,7 +1090,7 @@ static int wait_for_space(struct pipe_inode_info *pip=
e, unsigned flags)
 =09=09=09send_sig(SIGPIPE, current, 0);
 =09=09=09return -EPIPE;
 =09=09}
-=09=09if (!pipe_full(pipe->head, pipe->tail, pipe->ring_size))
+=09=09if (!pipe_full(pipe->head, pipe->tail, pipe->max_usage))
 =09=09=09return 0;
 =09=09if (flags & SPLICE_F_NONBLOCK)
 =09=09=09return -EAGAIN;
@@ -1498,13 +1498,13 @@ static int opipe_prep(struct pipe_inode_info *pipe,=
 unsigned int flags)
 =09 * Check ->nrbufs without the inode lock first. This function
 =09 * is speculative anyways, so missing one is ok.
 =09 */
-=09if (pipe_full(pipe->head, pipe->tail, pipe->ring_size))
+=09if (pipe_full(pipe->head, pipe->tail, pipe->max_usage))
 =09=09return 0;
=20
 =09ret =3D 0;
 =09pipe_lock(pipe);
=20
-=09while (pipe_full(pipe->head, pipe->tail, pipe->ring_size)) {
+=09while (pipe_full(pipe->head, pipe->tail, pipe->max_usage)) {
 =09=09if (!pipe->readers) {
 =09=09=09send_sig(SIGPIPE, current, 0);
 =09=09=09ret =3D -EPIPE;
@@ -1584,7 +1584,7 @@ static int splice_pipe_to_pipe(struct pipe_inode_info=
 *ipipe,
 =09=09 * pipe is empty or the output pipe is full.
 =09=09 */
 =09=09if (pipe_empty(i_head, i_tail) ||
-=09=09    pipe_full(o_head, o_tail, opipe->ring_size)) {
+=09=09    pipe_full(o_head, o_tail, opipe->max_usage)) {
 =09=09=09/* Already processed some buffers, break */
 =09=09=09if (ret)
 =09=09=09=09break;
@@ -1706,7 +1706,7 @@ static int link_pipe(struct pipe_inode_info *ipipe,
 =09=09 * output room, break.
 =09=09 */
 =09=09if (pipe_empty(i_head, i_tail) ||
-=09=09    pipe_full(o_head, o_tail, opipe->ring_size))
+=09=09    pipe_full(o_head, o_tail, opipe->max_usage))
 =09=09=09break;
=20
 =09=09ibuf =3D &ipipe->bufs[i_tail & i_mask];
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index fad096697ff5..90055ff16550 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -32,6 +32,7 @@ struct pipe_buffer {
  *=09@wait: reader/writer wait point in case of empty/full pipe
  *=09@head: The point of buffer production
  *=09@tail: The point of buffer consumption
+ *=09@max_usage: The maximum number of slots that may be used in the ring
  *=09@ring_size: total number of buffers (should be a power of 2)
  *=09@tmp_page: cached released page
  *=09@readers: number of current readers of this pipe
@@ -50,6 +51,7 @@ struct pipe_inode_info {
 =09wait_queue_head_t wait;
 =09unsigned int head;
 =09unsigned int tail;
+=09unsigned int max_usage;
 =09unsigned int ring_size;
 =09unsigned int readers;
 =09unsigned int writers;
@@ -176,9 +178,11 @@ static inline unsigned int pipe_space_for_user(unsigne=
d int head, unsigned int t
 =09unsigned int p_occupancy, p_space;
=20
 =09p_occupancy =3D pipe_occupancy(head, tail);
-=09if (p_occupancy >=3D pipe->ring_size)
+=09if (p_occupancy >=3D pipe->max_usage)
 =09=09return 0;
 =09p_space =3D pipe->ring_size - p_occupancy;
+=09if (p_space > pipe->max_usage)
+=09=09p_space =3D pipe->max_usage;
 =09return p_space;
 }
=20
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 150a40bdb21a..134737e9d4ee 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -395,7 +395,7 @@ static size_t copy_page_to_iter_pipe(struct page *page,=
 size_t offset, size_t by
 =09=09i_head++;
 =09=09buf =3D &pipe->bufs[i_head & p_mask];
 =09}
-=09if (pipe_full(i_head, p_tail, pipe->ring_size))
+=09if (pipe_full(i_head, p_tail, pipe->max_usage))
 =09=09return 0;
=20
 =09buf->ops =3D &page_cache_pipe_buf_ops;
@@ -528,7 +528,7 @@ static size_t push_pipe(struct iov_iter *i, size_t size=
,
 =09=09pipe->bufs[iter_head & p_mask].len =3D PAGE_SIZE;
 =09=09iter_head++;
 =09}
-=09while (!pipe_full(iter_head, p_tail, pipe->ring_size)) {
+=09while (!pipe_full(iter_head, p_tail, pipe->max_usage)) {
 =09=09struct pipe_buffer *buf =3D &pipe->bufs[iter_head & p_mask];
 =09=09struct page *page =3D alloc_page(GFP_USER);
 =09=09if (!page)