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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>
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parent
adb5c2473d
commit
7950e3852a
2 changed files with 50 additions and 20 deletions
61
fs/namei.c
61
fs/namei.c
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@ -119,40 +119,69 @@
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*/
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void final_putname(struct filename *name)
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{
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if (name->separate) {
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__putname(name->name);
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kfree(name);
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} else {
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__putname(name);
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}
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}
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#define EMBEDDED_NAME_MAX (PATH_MAX - sizeof(struct filename))
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static struct filename *
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getname_flags(const char __user *filename, int flags, int *empty)
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{
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struct filename *result, *err;
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char *kname;
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int len;
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long max;
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char *kname;
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result = audit_reusename(filename);
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if (result)
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return result;
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/* FIXME: create dedicated slabcache? */
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result = kzalloc(sizeof(*result), GFP_KERNEL);
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result = __getname();
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if (unlikely(!result))
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return ERR_PTR(-ENOMEM);
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kname = __getname();
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if (unlikely(!kname)) {
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err = ERR_PTR(-ENOMEM);
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goto error_free_name;
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}
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/*
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* First, try to embed the struct filename inside the names_cache
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* allocation
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*/
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kname = (char *)result + sizeof(*result);
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result->name = kname;
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result->uptr = filename;
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len = strncpy_from_user(kname, filename, PATH_MAX);
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result->separate = false;
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max = EMBEDDED_NAME_MAX;
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recopy:
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len = strncpy_from_user(kname, filename, max);
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if (unlikely(len < 0)) {
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err = ERR_PTR(len);
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goto error;
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}
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/*
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* Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
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* separate struct filename so we can dedicate the entire
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* names_cache allocation for the pathname, and re-do the copy from
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* userland.
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*/
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if (len == EMBEDDED_NAME_MAX && max == EMBEDDED_NAME_MAX) {
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kname = (char *)result;
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result = kzalloc(sizeof(*result), GFP_KERNEL);
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if (!result) {
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err = ERR_PTR(-ENOMEM);
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result = (struct filename *)kname;
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goto error;
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}
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result->name = kname;
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result->separate = true;
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max = PATH_MAX;
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goto recopy;
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}
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/* The empty path is special. */
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if (unlikely(!len)) {
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if (empty)
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@ -163,15 +192,15 @@ getname_flags(const char __user *filename, int flags, int *empty)
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}
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err = ERR_PTR(-ENAMETOOLONG);
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if (likely(len < PATH_MAX)) {
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if (unlikely(len >= PATH_MAX))
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goto error;
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result->uptr = filename;
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audit_getname(result);
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return result;
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}
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error:
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__putname(kname);
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error_free_name:
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kfree(result);
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final_putname(result);
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return err;
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}
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@ -2201,6 +2201,7 @@ struct filename {
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const char *name; /* pointer to actual string */
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const __user char *uptr; /* original userland pointer */
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struct audit_names *aname;
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bool separate; /* should "name" be freed? */
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};
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extern int do_truncate(struct dentry *, loff_t start, unsigned int time_attrs,
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