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From:   Christoph Hellwig <hch@lst.de>
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Cc:     Luis Chamberlain <mcgrof@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 09/23] fs: add a __kernel_read helper
Date:   Tue,  7 Jul 2020 19:47:47 +0200
Message-Id: <20200707174801.4162712-10-hch@lst.de>
In-Reply-To: <20200707174801.4162712-1-hch@lst.de>
References: <20200707174801.4162712-1-hch@lst.de>
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Sender: linux-kernel-owner@vger.kernel.org
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This is the counterpart to __kernel_write, and skip the rw_verify_area
call compared to kernel_read.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/read_write.c    | 23 +++++++++++++++++++++++
 include/linux/fs.h |  1 +
 2 files changed, 24 insertions(+)

diff --git a/fs/read_write.c b/fs/read_write.c
index bd46c959799e97..cc8e0b4f3cd697 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -430,6 +430,29 @@ ssize_t __vfs_read(struct file *file, char __user *buf, size_t count,
 		return -EINVAL;
 }
 
+ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
+{
+	mm_segment_t old_fs = get_fs();
+	ssize_t ret;
+
+	if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))
+		return -EINVAL;
+	if (!(file->f_mode & FMODE_CAN_READ))
+		return -EINVAL;
+
+	if (count > MAX_RW_COUNT)
+		count =  MAX_RW_COUNT;
+	set_fs(KERNEL_DS);
+	ret = __vfs_read(file, (void __user *)buf, count, pos);
+	set_fs(old_fs);
+	if (ret > 0) {
+		fsnotify_access(file);
+		add_rchar(current, ret);
+	}
+	inc_syscr(current);
+	return ret;
+}
+
 ssize_t kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
 {
 	mm_segment_t old_fs;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3f881a892ea746..22cbe7b2e91994 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3033,6 +3033,7 @@ extern int kernel_read_file_from_path_initns(const char *, void **, loff_t *, lo
 extern int kernel_read_file_from_fd(int, void **, loff_t *, loff_t,
 				    enum kernel_read_file_id);
 extern ssize_t kernel_read(struct file *, void *, size_t, loff_t *);
+ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos);
 extern ssize_t kernel_write(struct file *, const void *, size_t, loff_t *);
 extern ssize_t __kernel_write(struct file *, const void *, size_t, loff_t *);
 extern struct file * open_exec(const char *);
-- 
2.26.2