From c709c7ca020a52ef6530733a9a5f014bd6b71937 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() commit c42dd069be8dfc9b2239a5c89e73bbd08ab35de0 upstream. 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 Signed-off-by: Kyle Zeng Signed-off-by: Greg Kroah-Hartman --- fs/configfs/dir.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index 12388ed4faa5..0b7e9ab517d5 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -479,6 +479,7 @@ static struct dentry * configfs_lookup(struct inode *dir, if (!configfs_dirent_is_ready(parent_sd)) goto out; + spin_lock(&configfs_dirent_lock); list_for_each_entry(sd, &parent_sd->s_children, s_sibling) { if (sd->s_type & CONFIGFS_NOT_PINNED) { const unsigned char * name = configfs_get_name(sd); @@ -491,6 +492,7 @@ static struct dentry * configfs_lookup(struct inode *dir, break; } } + spin_unlock(&configfs_dirent_lock); if (!found) { /*