Commit c42dd069 authored by Sishuai Gong's avatar Sishuai Gong Committed by Christoph Hellwig
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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: default avatarSishuai Gong <sishuai@purdue.edu>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
parent d07f132a

fs/configfs/dir.c

+4 −3
Original line number Diff line number Diff line
@@ -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;

}