[PATCH 5.10 014/406] configfs: fix a race in configfs_lookup()

Greg Kroah-Hartman
2023-09-17T19:17:46Z

From: Sishuai Gong <sishuai@purdue.edu>

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 <sishuai@purdue.edu>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Kyle Zeng <zengyhkyle@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/configfs/dir.c | 2 ++
1 file changed, 2 insertions(+)

--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -479,6 +479,7 @@ static struct dentry * configfs_lookup(s
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(s
break;
}
}
+ spin_unlock(&configfs_dirent_lock);

if (!found) {
/*