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From: Hillf Danton <hdanton@sina.com>
To: syzbot <syzbot+d7c7a495a5e466c031b6@syzkaller.appspotmail.com>
Cc: linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [v9fs?] KASAN: slab-use-after-free Read in p9_fid_destroy
Date: Sat, 18 May 2024 19:41:05 +0800
Message-Id: <20240518114105.1730-1-hdanton@sina.com>
In-Reply-To: <00000000000049897e0618a4b1ff@google.com>
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On Fri, 17 May 2024 04:31:28 -0700
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    ea5f6ad9ad96 Merge tag 'platform-drivers-x86-v6.10-1' of g..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11df3084980000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  ea5f6ad9ad96

--- x/net/9p/client.c
+++ y/net/9p/client.c
@@ -879,15 +879,19 @@ static void p9_fid_destroy(struct p9_fid
 {
 	struct p9_client *clnt;
 	unsigned long flags;
+	bool empty;
 
 	p9_debug(P9_DEBUG_FID, "fid %d\n", fid->fid);
 	trace_9p_fid_ref(fid, P9_FID_REF_DESTROY);
 	clnt = fid->clnt;
 	spin_lock_irqsave(&clnt->lock, flags);
 	idr_remove(&clnt->fids, fid->fid);
+	empty = idr_is_empty(&clnt->fids) && clnt->status == Hung + 1;
 	spin_unlock_irqrestore(&clnt->lock, flags);
 	kfree(fid->rdir);
 	kfree(fid);
+	if (empty)
+		kfree(clnt);
 }
 
 /* We also need to export tracepoint symbols for tracepoint_enabled() */
@@ -1057,6 +1061,8 @@ EXPORT_SYMBOL(p9_client_create);
 void p9_client_destroy(struct p9_client *clnt)
 {
 	struct p9_fid *fid;
+	unsigned long flags;
+	bool empty;
 	int id;
 
 	p9_debug(P9_DEBUG_MUX, "clnt %p\n", clnt);
@@ -1068,13 +1074,18 @@ void p9_client_destroy(struct p9_client
 
 	idr_for_each_entry(&clnt->fids, fid, id) {
 		pr_info("Found fid %d not clunked\n", fid->fid);
-		p9_fid_destroy(fid);
 	}
 
 	p9_tag_cleanup(clnt);
 
 	kmem_cache_destroy(clnt->fcall_cache);
-	kfree(clnt);
+	spin_lock_irqsave(&clnt->lock, flags);
+	clnt->status = Hung + 1;
+	empty = idr_is_empty(&clnt->fids);
+	spin_unlock_irqrestore(&clnt->lock, flags);
+
+	if (empty)
+		kfree(clnt);
 }
 EXPORT_SYMBOL(p9_client_destroy);
 
--