[PATCH] configfs: fix a race in configfs_lookup()

[Kyle Zeng <zengyhkyle@gmail.com>]

commit c42dd069be8dfc9b2239a5c89e73bbd08ab35de0 upstream.
Backporting the patch to stable-v5.10.y to avoid race condition between configfs_dir_lseek and
configfs_lookup since they both operate ->s_childre and configfs_lookup
forgets to obtain the lock.
The patch deviates from the original patch because of code change.
The idea is to hold the configfs_dirent_lock when traversing
->s_children, which follows the core idea of the original patch.


Signed-off-by: Kyle Zeng <zengyhkyle@gmail.com>
---
 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) {
 		/*
-- 
2.34.1