linux-kernel - [PATCH 1/2] pipe: fix race with fcntl

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Message-Id: <1428858502-5371-2-git-send-email-dmonakhov@openvz.org>
Date:	Sun, 12 Apr 2015 21:08:21 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Cc:	linux-fsdevel@...r.kernel.org,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: [PATCH 1/2] pipe: fix race with fcntl

Fix other long standing issues caused by fcntl(,F_SETFL,):
- User can disable O_DIRECT for pipe[1] (paketized IO), but can not enable it again.
- Currently we do not set O_APPEND on pipe[1] (IMHO it is wrong, but let it be)
  so it is reasonable to completely prohibit change O_APPEND flag on both
  end's of pipe. Add ->check_flags method in order to diallow O_APPEND toggling.

Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
---
 fs/fcntl.c |    6 ++++--
 fs/pipe.c  |   16 +++++++++++++---
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index ee85cd4..0bdc9c7 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -51,9 +51,11 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
 	       if (arg & O_NDELAY)
 		   arg |= O_NONBLOCK;
 
+	/* allowed only for inodes with ->direct_io method or write pipe */
 	if (arg & O_DIRECT) {
-		if (!filp->f_mapping || !filp->f_mapping->a_ops ||
-			!filp->f_mapping->a_ops->direct_IO)
+		if ((!filp->f_mapping || !filp->f_mapping->a_ops ||
+		     !filp->f_mapping->a_ops->direct_IO) &&
+		    !(get_pipe_info(filp) && (filp->f_flags | O_WRONLY)))
 				return -EINVAL;
 	}
 
diff --git a/fs/pipe.c b/fs/pipe.c
index 8865f79..0c15647 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -329,9 +329,9 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 	return ret;
 }
 
-static inline int is_packetized(struct file *file)
+static inline int is_packetized(struct kiocb *iocb)
 {
-	return (file->f_flags & O_DIRECT) != 0;
+	return (iocb->ki_flags & IOCB_DIRECT) != 0;
 }
 
 static ssize_t
@@ -427,7 +427,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			buf->offset = 0;
 			buf->len = copied;
 			buf->flags = 0;
-			if (is_packetized(filp)) {
+			if (is_packetized(iocb)) {
 				buf->ops = &packet_pipe_buf_ops;
 				buf->flags = PIPE_BUF_FLAG_PACKET;
 			}
@@ -943,6 +943,15 @@ err:
 	return ret;
 }
 
+/* XXX: Currently it is not possible distinguish read side from write one */
+static int pipe_check_flags(int flags)
+{
+	if (flags & O_APPEND)
+	    return -EINVAL;
+
+	return 0;
+}
+
 const struct file_operations pipefifo_fops = {
 	.open		= fifo_open,
 	.llseek		= no_llseek,
@@ -952,6 +961,7 @@ const struct file_operations pipefifo_fops = {
 	.unlocked_ioctl	= pipe_ioctl,
 	.release	= pipe_release,
 	.fasync		= pipe_fasync,
+	.check_flags	= pipe_check_flags,
 };
 
 /*
-- 
1.7.1

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