linux-kernel - [PATCH 1/2] vfs: export symbol 'getname' and 'putname'

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Message-Id: <1429674624-25922-2-git-send-email-boqun.feng@gmail.com>
Date:	Wed, 22 Apr 2015 11:50:23 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	linux-fsdevel@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Cc:	Boqun Feng <boqun.feng@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jan Kara <jack@...e.cz>
Subject: [PATCH 1/2] vfs: export symbol 'getname' and 'putname'

getname/putname in fs/namei.c is a well-implemented way to copy a file
name from userland, however other ways, such as directly calling
__getname() and strncpy_from_user(), may lack features(e.g. auditing and
reusing), introduce errors or at least reinvent wheels. Therefore for
places need a kernel file name copy from userland, it's better to use
getname and putname if possible.

To be able to use these functions all over the kernel, symbols 'getname'
and 'putname' are exported and comments of their behaviors and
constraints are added.

Suggested-by: Al Viro <viro@...IV.linux.org.uk>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 fs/namei.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index c83145a..472911c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -199,11 +199,23 @@ error:
 	return err;
 }
 
+/**
+ * getname() - Get a file name copy from userland
+ * @filename: userland pointer to the file name
+ *
+ * If successful, return a 'struct filename' pointer and ->name is the pointer
+ * to the kernel copy of the file name, otherwise an ERR_PTR.
+ *
+ * getname() should only be called in a system call context, and for each
+ * getname() that returns a successful value, callers must ensure exactly one
+ * corresponding putname() is called before returning to userland.
+ */
 struct filename *
 getname(const char __user * filename)
 {
 	return getname_flags(filename, 0, NULL);
 }
+EXPORT_SYMBOL(getname);
 
 struct filename *
 getname_kernel(const char * filename)
@@ -242,6 +254,11 @@ getname_kernel(const char * filename)
 	return result;
 }
 
+/* putname() - Release a 'struct filename' structure
+ * @name: the 'struct filename' structure to be release
+ *
+ * See more at getname()
+ */
 void putname(struct filename *name)
 {
 	BUG_ON(name->refcnt <= 0);
@@ -255,6 +272,7 @@ void putname(struct filename *name)
 	} else
 		__putname(name);
 }
+EXPORT_SYMBOL(putname);
 
 static int check_acl(struct inode *inode, int mask)
 {
-- 
2.3.5

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