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Commit 7950e385 authored by Jeff Layton's avatar Jeff Layton Committed by Al Viro
Browse files

vfs: embed struct filename inside of names_cache allocation if possible 



In the common case where a name is much smaller than PATH_MAX, an extra
allocation for struct filename is unnecessary. Before allocating a
separate one, try to embed the struct filename inside the buffer first. If
it turns out that that's not long enough, then fall back to allocating a
separate struct filename and redoing the copy.

Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent adb5c247

fs/namei.c

+49 −20
Original line number Diff line number Diff line
@@ -119,40 +119,69 @@ 
 */

void final_putname(struct filename *name)

{

	if (name->separate) {

		__putname(name->name);

		kfree(name);

	} else {

		__putname(name);

	}

}



#define EMBEDDED_NAME_MAX	(PATH_MAX - sizeof(struct filename))



static struct filename *

getname_flags(const char __user *filename, int flags, int *empty)

{

	struct filename *result, *err;

	char *kname;

	int len;

	long max;

	char *kname;



	result = audit_reusename(filename);

	if (result)

		return result;



	/* FIXME: create dedicated slabcache? */

	result = kzalloc(sizeof(*result), GFP_KERNEL);

	result = __getname();

	if (unlikely(!result))

		return ERR_PTR(-ENOMEM);



	kname = __getname();

	if (unlikely(!kname)) {

		err = ERR_PTR(-ENOMEM);

		goto error_free_name;

	}



	/*

	 * First, try to embed the struct filename inside the names_cache

	 * allocation

	 */

	kname = (char *)result + sizeof(*result);

	result->name = kname;

	result->uptr = filename;

	len = strncpy_from_user(kname, filename, PATH_MAX);

	result->separate = false;

	max = EMBEDDED_NAME_MAX;



recopy:

	len = strncpy_from_user(kname, filename, max);

	if (unlikely(len < 0)) {

		err = ERR_PTR(len);

		goto error;

	}



	/*

	 * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a

	 * separate struct filename so we can dedicate the entire

	 * names_cache allocation for the pathname, and re-do the copy from

	 * userland.

	 */

	if (len == EMBEDDED_NAME_MAX && max == EMBEDDED_NAME_MAX) {

		kname = (char *)result;



		result = kzalloc(sizeof(*result), GFP_KERNEL);

		if (!result) {

			err = ERR_PTR(-ENOMEM);

			result = (struct filename *)kname;

			goto error;

		}

		result->name = kname;

		result->separate = true;

		max = PATH_MAX;

		goto recopy;

	}



	/* The empty path is special. */

	if (unlikely(!len)) {

		if (empty)
@@ -163,15 +192,15 @@ getname_flags(const char __user *filename, int flags, int *empty) 
	}



	err = ERR_PTR(-ENAMETOOLONG);

	if (likely(len < PATH_MAX)) {

	if (unlikely(len >= PATH_MAX))

		goto error;



	result->uptr = filename;

	audit_getname(result);

	return result;

	}



error:

	__putname(kname);

error_free_name:

	kfree(result);

	final_putname(result);

	return err;

}

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -2201,6 +2201,7 @@ struct filename { 
	const char		*name;	/* pointer to actual string */

	const __user char	*uptr;	/* original userland pointer */

	struct audit_names	*aname;

	bool			separate; /* should "name" be freed? */

};



extern int do_truncate(struct dentry *, loff_t start, unsigned int time_attrs,