Acked-by: Joel Becker <jlbec@xxxxxxxxxxxx>
On Wed, Aug 25, 2021 at 08:49:06AM +0200, Christoph Hellwig wrote:
> From: Sishuai Gong <sishuai@xxxxxxxxxx>
>
> 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 <sishuai@xxxxxxxxxx>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> 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;
> }
> --
> 2.30.2
>
--
