linux-ext4 - [PATCH 01/13] fs/super.c: don't drop ->s_user_ns until we free struct super

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Date: Sun,  4 Feb 2024 02:17:27 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: linux-fsdevel@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Christian Brauner <brauner@...nel.org>,
	linux-ext4@...r.kernel.org,
	linux-nfs@...r.kernel.org,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-cifs@...r.kernel.org
Subject: [PATCH 01/13] fs/super.c: don't drop ->s_user_ns until we free struct super_block itself

Avoids fun races in RCU pathwalk...  Same goes for freeing LSM shite
hanging off super_block's arse.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/super.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index d35e85295489..d6efeba0d0ce 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -274,9 +274,10 @@ static void destroy_super_work(struct work_struct *work)
 {
 	struct super_block *s = container_of(work, struct super_block,
 							destroy_work);
-	int i;
-
-	for (i = 0; i < SB_FREEZE_LEVELS; i++)
+	security_sb_free(s);
+	put_user_ns(s->s_user_ns);
+	kfree(s->s_subtype);
+	for (int i = 0; i < SB_FREEZE_LEVELS; i++)
 		percpu_free_rwsem(&s->s_writers.rw_sem[i]);
 	kfree(s);
 }
@@ -296,9 +297,6 @@ static void destroy_unused_super(struct super_block *s)
 	super_unlock_excl(s);
 	list_lru_destroy(&s->s_dentry_lru);
 	list_lru_destroy(&s->s_inode_lru);
-	security_sb_free(s);
-	put_user_ns(s->s_user_ns);
-	kfree(s->s_subtype);
 	shrinker_free(s->s_shrink);
 	/* no delays needed */
 	destroy_super_work(&s->destroy_work);
@@ -409,9 +407,6 @@ static void __put_super(struct super_block *s)
 		WARN_ON(s->s_dentry_lru.node);
 		WARN_ON(s->s_inode_lru.node);
 		WARN_ON(!list_empty(&s->s_mounts));
-		security_sb_free(s);
-		put_user_ns(s->s_user_ns);
-		kfree(s->s_subtype);
 		call_rcu(&s->rcu, destroy_super_rcu);
 	}
 }
-- 
2.39.2