[PATCH 06/13] fs: implement kernel_write using __kernel_write

From: Christoph Hellwig <hch@lst.de>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Ian Kent <raven@themaw.net>, David Howells <dhowells@redhat.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	netfilter-devel@vger.kernel.org
Subject: [PATCH 06/13] fs: implement kernel_write using __kernel_write
Date: Mon, 15 Jun 2020 14:12:50 +0200	[thread overview]
Message-ID: <20200615121257.798894-7-hch@lst.de> (raw)
In-Reply-To: <20200615121257.798894-1-hch@lst.de>

Consolidate the two in-kernel write helpers to make upcoming changes
easier.  The only difference are the missing call to rw_verify_area
in kernel_write, and an access_ok check that doesn't make sense for
kernel buffers to start with.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/read_write.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 76be155ad98242..9d50d3cec017d8 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -499,6 +499,7 @@ static ssize_t __vfs_write(struct file *file, const char __user *p,
 		return -EINVAL;
 }
 
+/* caller is responsible for file_start_write/file_end_write */
 ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos)
 {
 	mm_segment_t old_fs;
@@ -528,16 +529,16 @@ ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t
 ssize_t kernel_write(struct file *file, const void *buf, size_t count,
 			    loff_t *pos)
 {
-	mm_segment_t old_fs;
-	ssize_t res;
+	ssize_t ret;
 
-	old_fs = get_fs();
-	set_fs(KERNEL_DS);
-	/* The cast to a user pointer is valid due to the set_fs() */
-	res = vfs_write(file, (__force const char __user *)buf, count, pos);
-	set_fs(old_fs);
+	ret = rw_verify_area(WRITE, file, pos, count);
+	if (ret)
+		return ret;
 
-	return res;
+	file_start_write(file);
+	ret =  __kernel_write(file, buf, count, pos);
+	file_end_write(file);
+	return ret;
 }
 EXPORT_SYMBOL(kernel_write);
 
-- 
2.26.2

