VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
};
-static LIST_HEAD(entries);
-static int enabled = 1;
-
enum {Enabled, Magic};
#define MISC_FMT_PRESERVE_ARGV0 (1UL << 31)
#define MISC_FMT_OPEN_BINARY (1UL << 30)
char *name;
struct dentry *dentry;
struct file *interp_file;
+ refcount_t users; /* sync removal with load_misc_binary() */
} Node;
-static DEFINE_RWLOCK(entries_lock);
static struct file_system_type bm_fs_type;
-static struct vfsmount *bm_mnt;
-static int entry_count;
/*
* Max length of the register string. Determined by:
*/
#define MAX_REGISTER_LENGTH 1920
-/*
- * Check if we support the binfmt
- * if we do, return the node, else NULL
- * locking is done in load_misc_binary
+/**
+ * search_binfmt_handler - search for a binary handler for @bprm
+ * @misc: handle to binfmt_misc instance
+ * @bprm: binary for which we are looking for a handler
+ *
+ * Search for a binary type handler for @bprm in the list of registered binary
+ * type handlers.
+ *
+ * Return: binary type list entry on success, NULL on failure
*/
-static Node *check_file(struct linux_binprm *bprm)
+static Node *search_binfmt_handler(struct binfmt_misc *misc,
+ struct linux_binprm *bprm)
{
char *p = strrchr(bprm->interp, '.');
- struct list_head *l;
+ Node *e;
/* Walk all the registered handlers. */
- list_for_each(l, &entries) {
- Node *e = list_entry(l, Node, list);
+ list_for_each_entry(e, &misc->entries, list) {
char *s;
int j;
if (j == e->size)
return e;
}
+
return NULL;
}
+/**
+ * get_binfmt_handler - try to find a binary type handler
+ * @misc: handle to binfmt_misc instance
+ * @bprm: binary for which we are looking for a handler
+ *
+ * Try to find a binfmt handler for the binary type. If one is found take a
+ * reference to protect against removal via bm_{entry,status}_write().
+ *
+ * Return: binary type list entry on success, NULL on failure
+ */
+static Node *get_binfmt_handler(struct binfmt_misc *misc,
+ struct linux_binprm *bprm)
+{
+ Node *e;
+
+ read_lock(&misc->entries_lock);
+ e = search_binfmt_handler(misc, bprm);
+ if (e)
+ refcount_inc(&e->users);
+ read_unlock(&misc->entries_lock);
+ return e;
+}
+
+/**
+ * put_binfmt_handler - put binary handler node
+ * @e: node to put
+ *
+ * Free node syncing with load_misc_binary() and defer final free to
+ * load_misc_binary() in case it is using the binary type handler we were
+ * requested to remove.
+ */
+static void put_binfmt_handler(Node *e)
+{
+ if (refcount_dec_and_test(&e->users)) {
+ if (e->flags & MISC_FMT_OPEN_FILE)
+ filp_close(e->interp_file, NULL);
+ kfree(e);
+ }
+}
+
+/**
+ * load_binfmt_misc - load the binfmt_misc of the caller's user namespace
+ *
+ * To be called in load_misc_binary() to load the relevant struct binfmt_misc.
+ * If a user namespace doesn't have its own binfmt_misc mount it can make use
+ * of its ancestor's binfmt_misc handlers. This mimicks the behavior of
+ * pre-namespaced binfmt_misc where all registered binfmt_misc handlers where
+ * available to all user and user namespaces on the system.
+ *
+ * Return: the binfmt_misc instance of the caller's user namespace
+ */
+static struct binfmt_misc *load_binfmt_misc(void)
+{
+ const struct user_namespace *user_ns;
+ struct binfmt_misc *misc;
+
+ user_ns = current_user_ns();
+ while (user_ns) {
+ /* Pairs with smp_store_release() in bm_fill_super(). */
+ misc = smp_load_acquire(&user_ns->binfmt_misc);
+ if (misc)
+ return misc;
+
+ user_ns = user_ns->parent;
+ }
+
+ return &init_binfmt_misc;
+}
+
/*
* the loader itself
*/
{
Node *fmt;
struct file *interp_file = NULL;
- int retval;
+ int retval = -ENOEXEC;
+ struct binfmt_misc *misc;
- retval = -ENOEXEC;
- if (!enabled)
+ misc = load_binfmt_misc();
+ if (!misc->enabled)
return retval;
- /* to keep locking time low, we copy the interpreter string */
- read_lock(&entries_lock);
- fmt = check_file(bprm);
- if (fmt)
- dget(fmt->dentry);
- read_unlock(&entries_lock);
+ fmt = get_binfmt_handler(misc, bprm);
if (!fmt)
return retval;
retval = 0;
ret:
- dput(fmt->dentry);
+
+ /*
+ * If we actually put the node here all concurrent calls to
+ * load_misc_binary() will have finished. We also know
+ * that for the refcount to be zero someone must have concurently
+ * removed the binary type handler from the list and it's our job to
+ * free it.
+ */
+ put_binfmt_handler(fmt);
+
return retval;
}
err = -ENOMEM;
memsize = sizeof(Node) + count + 8;
- e = kmalloc(memsize, GFP_KERNEL);
+ e = kmalloc(memsize, GFP_KERNEL_ACCOUNT);
if (!e)
goto out;
if (e->mask) {
int i;
- char *masked = kmalloc(e->size, GFP_KERNEL);
+ char *masked = kmalloc(e->size, GFP_KERNEL_ACCOUNT);
print_hex_dump_bytes(
KBUILD_MODNAME ": register: mask[decoded]: ",
return inode;
}
+/**
+ * i_binfmt_misc - retrieve struct binfmt_misc from a binfmt_misc inode
+ * @inode: inode of the relevant binfmt_misc instance
+ *
+ * This helper retrieves struct binfmt_misc from a binfmt_misc inode. This can
+ * be done without any memory barriers because we are guaranteed that
+ * user_ns->binfmt_misc is fully initialized. It was fully initialized when the
+ * binfmt_misc mount was first created.
+ *
+ * Return: struct binfmt_misc of the relevant binfmt_misc instance
+ */
+static struct binfmt_misc *i_binfmt_misc(struct inode *inode)
+{
+ return inode->i_sb->s_user_ns->binfmt_misc;
+}
+
+/**
+ * bm_evict_inode - cleanup data associated with @inode
+ * @inode: inode to which the data is attached
+ *
+ * Cleanup the binary type handler data associated with @inode if a binary type
+ * entry is removed or the filesystem is unmounted and the super block is
+ * shutdown.
+ *
+ * If the ->evict call was not caused by a super block shutdown but by a write
+ * to remove the entry or all entries via bm_{entry,status}_write() the entry
+ * will have already been removed from the list. We keep the list_empty() check
+ * to make that explicit.
+*/
static void bm_evict_inode(struct inode *inode)
{
Node *e = inode->i_private;
- if (e && e->flags & MISC_FMT_OPEN_FILE)
- filp_close(e->interp_file, NULL);
-
clear_inode(inode);
- kfree(e);
+
+ if (e) {
+ struct binfmt_misc *misc;
+
+ misc = i_binfmt_misc(inode);
+ write_lock(&misc->entries_lock);
+ if (!list_empty(&e->list))
+ list_del_init(&e->list);
+ write_unlock(&misc->entries_lock);
+ put_binfmt_handler(e);
+ }
}
-static void kill_node(Node *e)
+/**
+ * unlink_binfmt_dentry - remove the dentry for the binary type handler
+ * @dentry: dentry associated with the binary type handler
+ *
+ * Do the actual filesystem work to remove a dentry for a registered binary
+ * type handler. Since binfmt_misc only allows simple files to be created
+ * directly under the root dentry of the filesystem we ensure that we are
+ * indeed passed a dentry directly beneath the root dentry, that the inode
+ * associated with the root dentry is locked, and that it is a regular file we
+ * are asked to remove.
+ */
+static void unlink_binfmt_dentry(struct dentry *dentry)
{
- struct dentry *dentry;
+ struct dentry *parent = dentry->d_parent;
+ struct inode *inode, *parent_inode;
- write_lock(&entries_lock);
- list_del_init(&e->list);
- write_unlock(&entries_lock);
+ /* All entries are immediate descendants of the root dentry. */
+ if (WARN_ON_ONCE(dentry->d_sb->s_root != parent))
+ return;
- dentry = e->dentry;
- drop_nlink(d_inode(dentry));
- d_drop(dentry);
- dput(dentry);
- simple_release_fs(&bm_mnt, &entry_count);
+ /* We only expect to be called on regular files. */
+ inode = d_inode(dentry);
+ if (WARN_ON_ONCE(!S_ISREG(inode->i_mode)))
+ return;
+
+ /* The parent inode must be locked. */
+ parent_inode = d_inode(parent);
+ if (WARN_ON_ONCE(!inode_is_locked(parent_inode)))
+ return;
+
+ if (simple_positive(dentry)) {
+ dget(dentry);
+ simple_unlink(parent_inode, dentry);
+ d_delete(dentry);
+ dput(dentry);
+ }
+}
+
+/**
+ * remove_binfmt_handler - remove a binary type handler
+ * @misc: handle to binfmt_misc instance
+ * @e: binary type handler to remove
+ *
+ * Remove a binary type handler from the list of binary type handlers and
+ * remove its associated dentry. This is called from
+ * binfmt_{entry,status}_write(). In the future, we might want to think about
+ * adding a proper ->unlink() method to binfmt_misc instead of forcing caller's
+ * to use writes to files in order to delete binary type handlers. But it has
+ * worked for so long that it's not a pressing issue.
+ */
+static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e)
+{
+ write_lock(&misc->entries_lock);
+ list_del_init(&e->list);
+ write_unlock(&misc->entries_lock);
+ unlink_binfmt_dentry(e->dentry);
}
/* /<entry> */
static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
size_t count, loff_t *ppos)
{
- struct dentry *root;
- Node *e = file_inode(file)->i_private;
+ struct inode *inode = file_inode(file);
+ Node *e = inode->i_private;
int res = parse_command(buffer, count);
switch (res) {
break;
case 3:
/* Delete this handler. */
- root = file_inode(file)->i_sb->s_root;
- inode_lock(d_inode(root));
+ inode = d_inode(inode->i_sb->s_root);
+ inode_lock(inode);
+ /*
+ * In order to add new element or remove elements from the list
+ * via bm_{entry,register,status}_write() inode_lock() on the
+ * root inode must be held.
+ * The lock is exclusive ensuring that the list can't be
+ * modified. Only load_misc_binary() can access but does so
+ * read-only. So we only need to take the write lock when we
+ * actually remove the entry from the list.
+ */
if (!list_empty(&e->list))
- kill_node(e);
+ remove_binfmt_handler(i_binfmt_misc(inode), e);
- inode_unlock(d_inode(root));
+ inode_unlock(inode);
break;
default:
return res;
struct inode *inode;
struct super_block *sb = file_inode(file)->i_sb;
struct dentry *root = sb->s_root, *dentry;
+ struct binfmt_misc *misc;
int err = 0;
struct file *f = NULL;
return PTR_ERR(e);
if (e->flags & MISC_FMT_OPEN_FILE) {
+ const struct cred *old_cred;
+
+ /*
+ * Now that we support unprivileged binfmt_misc mounts make
+ * sure we use the credentials that the register @file was
+ * opened with to also open the interpreter. Before that this
+ * didn't matter much as only a privileged process could open
+ * the register file.
+ */
+ old_cred = override_creds(file->f_cred);
f = open_exec(e->interpreter);
+ revert_creds(old_cred);
if (IS_ERR(f)) {
pr_notice("register: failed to install interpreter file %s\n",
e->interpreter);
if (!inode)
goto out2;
- err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
- if (err) {
- iput(inode);
- inode = NULL;
- goto out2;
- }
-
+ refcount_set(&e->users, 1);
e->dentry = dget(dentry);
inode->i_private = e;
inode->i_fop = &bm_entry_operations;
d_instantiate(dentry, inode);
- write_lock(&entries_lock);
- list_add(&e->list, &entries);
- write_unlock(&entries_lock);
+ misc = i_binfmt_misc(inode);
+ write_lock(&misc->entries_lock);
+ list_add(&e->list, &misc->entries);
+ write_unlock(&misc->entries_lock);
err = 0;
out2:
static ssize_t
bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
- char *s = enabled ? "enabled\n" : "disabled\n";
+ struct binfmt_misc *misc;
+ char *s;
+ misc = i_binfmt_misc(file_inode(file));
+ s = misc->enabled ? "enabled\n" : "disabled\n";
return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
}
static ssize_t bm_status_write(struct file *file, const char __user *buffer,
size_t count, loff_t *ppos)
{
+ struct binfmt_misc *misc;
int res = parse_command(buffer, count);
- struct dentry *root;
+ Node *e, *next;
+ struct inode *inode;
+ misc = i_binfmt_misc(file_inode(file));
switch (res) {
case 1:
/* Disable all handlers. */
- enabled = 0;
+ misc->enabled = false;
break;
case 2:
/* Enable all handlers. */
- enabled = 1;
+ misc->enabled = true;
break;
case 3:
/* Delete all handlers. */
- root = file_inode(file)->i_sb->s_root;
- inode_lock(d_inode(root));
+ inode = d_inode(file_inode(file)->i_sb->s_root);
+ inode_lock(inode);
- while (!list_empty(&entries))
- kill_node(list_first_entry(&entries, Node, list));
+ /*
+ * In order to add new element or remove elements from the list
+ * via bm_{entry,register,status}_write() inode_lock() on the
+ * root inode must be held.
+ * The lock is exclusive ensuring that the list can't be
+ * modified. Only load_misc_binary() can access but does so
+ * read-only. So we only need to take the write lock when we
+ * actually remove the entry from the list.
+ */
+ list_for_each_entry_safe(e, next, &misc->entries, list)
+ remove_binfmt_handler(misc, e);
- inode_unlock(d_inode(root));
+ inode_unlock(inode);
break;
default:
return res;
/* Superblock handling */
+static void bm_put_super(struct super_block *sb)
+{
+ struct user_namespace *user_ns = sb->s_fs_info;
+
+ sb->s_fs_info = NULL;
+ put_user_ns(user_ns);
+}
+
static const struct super_operations s_ops = {
.statfs = simple_statfs,
.evict_inode = bm_evict_inode,
+ .put_super = bm_put_super,
};
static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
{
int err;
+ struct user_namespace *user_ns = sb->s_user_ns;
+ struct binfmt_misc *misc;
static const struct tree_descr bm_files[] = {
[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
[3] = {"register", &bm_register_operations, S_IWUSR},
/* last one */ {""}
};
+ if (WARN_ON(user_ns != current_user_ns()))
+ return -EINVAL;
+
+ /*
+ * Lazily allocate a new binfmt_misc instance for this namespace, i.e.
+ * do it here during the first mount of binfmt_misc. We don't need to
+ * waste memory for every user namespace allocation. It's likely much
+ * more common to not mount a separate binfmt_misc instance than it is
+ * to mount one.
+ *
+ * While multiple superblocks can exist they are keyed by userns in
+ * s_fs_info for binfmt_misc. Hence, the vfs guarantees that
+ * bm_fill_super() is called exactly once whenever a binfmt_misc
+ * superblock for a userns is created. This in turn lets us conclude
+ * that when a binfmt_misc superblock is created for the first time for
+ * a userns there's no one racing us. Therefore we don't need any
+ * barriers when we dereference binfmt_misc.
+ */
+ misc = user_ns->binfmt_misc;
+ if (!misc) {
+ /*
+ * If it turns out that most user namespaces actually want to
+ * register their own binary type handler and therefore all
+ * create their own separate binfm_misc mounts we should
+ * consider turning this into a kmem cache.
+ */
+ misc = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL);
+ if (!misc)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&misc->entries);
+ rwlock_init(&misc->entries_lock);
+
+ /* Pairs with smp_load_acquire() in load_binfmt_misc(). */
+ smp_store_release(&user_ns->binfmt_misc, misc);
+ }
+
+ /*
+ * When the binfmt_misc superblock for this userns is shutdown
+ * ->enabled might have been set to false and we don't reinitialize
+ * ->enabled again in put_super() as someone might already be mounting
+ * binfmt_misc again. It also would be pointless since by the time
+ * ->put_super() is called we know that the binary type list for this
+ * bintfmt_misc mount is empty making load_misc_binary() return
+ * -ENOEXEC independent of whether ->enabled is true. Instead, if
+ * someone mounts binfmt_misc for the first time or again we simply
+ * reset ->enabled to true.
+ */
+ misc->enabled = true;
+
err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
if (!err)
sb->s_op = &s_ops;
return err;
}
+static void bm_free(struct fs_context *fc)
+{
+ if (fc->s_fs_info)
+ put_user_ns(fc->s_fs_info);
+}
+
static int bm_get_tree(struct fs_context *fc)
{
- return get_tree_single(fc, bm_fill_super);
+ return get_tree_keyed(fc, bm_fill_super, get_user_ns(fc->user_ns));
}
static const struct fs_context_operations bm_context_ops = {
+ .free = bm_free,
.get_tree = bm_get_tree,
};
.owner = THIS_MODULE,
.name = "binfmt_misc",
.init_fs_context = bm_init_fs_context,
+ .fs_flags = FS_USERNS_MOUNT,
.kill_sb = kill_litter_super,
};
MODULE_ALIAS_FS("binfmt_misc");
projects / linux-block.git / blobdiff