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: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jeff Layton 2012-10-10 16:43:13 -04:00 committed by Al Viro
parent adb5c2473d
commit 7950e3852a
2 changed files with 50 additions and 20 deletions

View file

@ -119,40 +119,69 @@
*/
void final_putname(struct filename *name)
{
__putname(name->name);
kfree(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)) {
audit_getname(result);
return result;
}
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;
}

View file

@ -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,