Re: [syzbot] [v9fs?] KASAN: slab-use-after-free Read in p9_fid_destroy

[Hillf Danton <hdanton@sina.com>]

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/include/net/9p/client.h
+++ y/include/net/9p/client.h
@@ -11,6 +11,7 @@
 
 #include <linux/utsname.h>
 #include <linux/idr.h>
+#include <linux/mutex.h>
 #include <linux/tracepoint-defs.h>
 
 /* Number of requests per row */
@@ -122,6 +123,7 @@ struct p9_client {
 
 	struct idr fids;
 	struct idr reqs;
+	struct mutex destroy_mutex;
 
 	char name[__NEW_UTS_LEN + 1];
 };
--- x/net/9p/client.c
+++ y/net/9p/client.c
@@ -1041,6 +1041,7 @@ struct p9_client *p9_client_create(const
 					   0, 0, P9_HDRSZ + 4,
 					   clnt->msize - (P9_HDRSZ + 4),
 					   NULL);
+	mutex_init(&clnt->destroy_mutex);
 
 	return clnt;
 
@@ -1058,6 +1059,7 @@ void p9_client_destroy(struct p9_client
 {
 	struct p9_fid *fid;
 	int id;
+	int clean;
 
 	p9_debug(P9_DEBUG_MUX, "clnt %p\n", clnt);
 
@@ -1066,9 +1068,18 @@ void p9_client_destroy(struct p9_client
 
 	v9fs_put_trans(clnt->trans_mod);
 
+again:
+	clean = 1;
+	mutex_lock(&clnt->destroy_mutex);
 	idr_for_each_entry(&clnt->fids, fid, id) {
 		pr_info("Found fid %d not clunked\n", fid->fid);
-		p9_fid_destroy(fid);
+		clean = 0;
+		break;
+	}
+	mutex_unlock(&clnt->destroy_mutex);
+	if (!clean) {
+		schedule_timeout_idle(2);
+		goto again;
 	}
 
 	p9_tag_cleanup(clnt);
@@ -1454,7 +1465,9 @@ error:
 		if (retries++ == 0)
 			goto again;
 	} else {
+		mutex_lock(&clnt->destroy_mutex);
 		p9_fid_destroy(fid);
+		mutex_unlock(&clnt->destroy_mutex);
 	}
 	return err;
 }
--