diff options
| -rw-r--r-- | fs/binfmt_misc.c | 216 |
1 files changed, 168 insertions, 48 deletions
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index e0108d17b085..cf5ed5cd4102 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -60,12 +60,11 @@ typedef struct { 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: @@ -82,19 +81,23 @@ static int entry_count; */ #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 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, &entries, list) { char *s; int j; @@ -123,9 +126,49 @@ static Node *check_file(struct linux_binprm *bprm) 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 linux_binprm *bprm) +{ + Node *e; + + read_lock(&entries_lock); + e = search_binfmt_handler(bprm); + if (e) + refcount_inc(&e->users); + read_unlock(&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); + } +} + /* * the loader itself */ @@ -139,12 +182,7 @@ static int load_misc_binary(struct linux_binprm *bprm) if (!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(bprm); if (!fmt) return retval; @@ -198,7 +236,16 @@ static int load_misc_binary(struct linux_binprm *bprm) 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 ->evict_inode() must have removed + * the node to be deleted from the list. All that is left for us is to + * close and free. + */ + put_binfmt_handler(fmt); + return retval; } @@ -552,30 +599,90 @@ static struct inode *bm_get_inode(struct super_block *sb, int mode) return inode; } +/** + * 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) { + write_lock(&entries_lock); + if (!list_empty(&e->list)) + list_del_init(&e->list); + write_unlock(&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; + + /* All entries are immediate descendants of the root dentry. */ + if (WARN_ON_ONCE(dentry->d_sb->s_root != parent)) + return; + /* 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(Node *e) +{ write_lock(&entries_lock); list_del_init(&e->list); write_unlock(&entries_lock); - - dentry = e->dentry; - drop_nlink(d_inode(dentry)); - d_drop(dentry); - dput(dentry); - simple_release_fs(&bm_mnt, &entry_count); + unlink_binfmt_dentry(e->dentry); } /* /<entry> */ @@ -602,8 +709,8 @@ bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) 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) { @@ -617,13 +724,22 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, 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(e); - inode_unlock(d_inode(root)); + inode_unlock(inode); break; default: return res; @@ -682,13 +798,7 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, 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; @@ -732,7 +842,8 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos) { int res = parse_command(buffer, count); - struct dentry *root; + Node *e, *next; + struct inode *inode; switch (res) { case 1: @@ -745,13 +856,22 @@ static ssize_t bm_status_write(struct file *file, const char __user *buffer, 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, &entries, list) + remove_binfmt_handler(e); - inode_unlock(d_inode(root)); + inode_unlock(inode); break; default: return res; |