From c42dd069be8dfc9b2239a5c89e73bbd08ab35de0 Mon Sep 17 00:00:00 2001 From: Sishuai Gong Date: Wed, 25 Aug 2021 07:52:20 +0200 Subject: [PATCH] configfs: fix a race in configfs_lookup() When configfs_lookup() is executing list_for_each_entry(), it is possible that configfs_dir_lseek() is calling list_del(). Some unfortunate interleavings of them can cause a kernel NULL pointer dereference error Thread 1 Thread 2 //configfs_dir_lseek() //configfs_lookup() list_del(&cursor->s_sibling); list_for_each_entry(sd, ...) Fix this by grabbing configfs_dirent_lock in configfs_lookup() while iterating ->s_children. Signed-off-by: Sishuai Gong Signed-off-by: Christoph Hellwig --- fs/configfs/dir.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index fc20bd8a6337..1466b5d01cbb 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -439,13 +439,13 @@ static struct dentry * configfs_lookup(struct inode *dir, if (!configfs_dirent_is_ready(parent_sd)) return ERR_PTR(-ENOENT); + spin_lock(&configfs_dirent_lock); list_for_each_entry(sd, &parent_sd->s_children, s_sibling) { if ((sd->s_type & CONFIGFS_NOT_PINNED) && !strcmp(configfs_get_name(sd), dentry->d_name.name)) { struct configfs_attribute *attr = sd->s_element; umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG; - spin_lock(&configfs_dirent_lock); dentry->d_fsdata = configfs_get(sd); sd->s_dentry = dentry; spin_unlock(&configfs_dirent_lock); @@ -462,10 +462,11 @@ static struct dentry * configfs_lookup(struct inode *dir, inode->i_size = PAGE_SIZE; inode->i_fop = &configfs_file_operations; } - break; + goto done; } } - + spin_unlock(&configfs_dirent_lock); +done: d_add(dentry, inode); return NULL; }