linux-kernel - [PATCH 04/11] fs: implement kernel_write using __kernel

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Date:   Fri,  8 May 2020 11:22:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: [PATCH 04/11] fs: implement kernel_write using __kernel_write

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@....de>
---
 fs/read_write.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index d91fe7ff6cc55..6b456a257b31c 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -531,16 +531,13 @@ EXPORT_SYMBOL(__kernel_write);
 ssize_t kernel_write(struct file *file, const void *buf, size_t count,
 			    loff_t *pos)
 {
-	mm_segment_t old_fs;
-	ssize_t res;
 
-	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);
+	ssize_t ret;
 
-	return res;
+	ret = rw_verify_area(WRITE, file, pos, count);
+	if (ret)
+		return ret;
+	return __kernel_write(file, buf, count, pos);
 }
 EXPORT_SYMBOL(kernel_write);
 
-- 
2.26.2