Re: [syzbot] [netfs?] KASAN: slab-use-after-free Read in iov_iter_advance

[Hillf Danton <hdanton@sina.com>]

On Fri, 20 Sep 2024 07:26:34 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    a430d95c5efa Merge tag 'lsm-pr-20240911' of git://git.kern..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10c7d69f980000

#syz test

--- x/fs/netfs/write_collect.c
+++ y/fs/netfs/write_collect.c
@@ -548,7 +548,9 @@ void netfs_write_collection_worker(struc
 		return;
 	}
 
+	mutex_lock(&ictx->wb_lock);
 	netfs_collect_write_results(wreq);
+	mutex_unlock(&ictx->wb_lock);
 
 	/* We're done when the app thread has finished posting subreqs and all
 	 * the queues in all the streams are empty.
--- l/net/9p/client.c
+++ c/net/9p/client.c
@@ -8,6 +8,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/sprintf.h>
 #include <linux/module.h>
 #include <linux/errno.h>
 #include <linux/fs.h>
@@ -979,6 +980,7 @@ struct p9_client *p9_client_create(const
 	int err;
 	struct p9_client *clnt;
 	char *client_id;
+	static int fcc = 0;
 
 	clnt = kmalloc(sizeof(*clnt), GFP_KERNEL);
 	if (!clnt)
@@ -991,6 +993,11 @@ struct p9_client *p9_client_create(const
 	client_id = utsname()->nodename;
 	memcpy(clnt->name, client_id, strlen(client_id) + 1);
 
+	clnt->name[__NEW_UTS_LEN] = 0;
+	if (__NEW_UTS_LEN <= snprintf(clnt->name, __NEW_UTS_LEN, "9pfcc%d", ++fcc)) {
+		kfree(clnt);
+		return ERR_PTR(-ENOMEM);
+	}
 	spin_lock_init(&clnt->lock);
 	idr_init(&clnt->fids);
 	idr_init(&clnt->reqs);
@@ -1039,7 +1046,7 @@ struct p9_client *p9_client_create(const
 	 * followed by data accessed from userspace by read
 	 */
 	clnt->fcall_cache =
-		kmem_cache_create_usercopy("9p-fcall-cache", clnt->msize,
+		kmem_cache_create_usercopy(clnt->name, clnt->msize,
 					   0, 0, P9_HDRSZ + 4,
 					   clnt->msize - (P9_HDRSZ + 4),
 					   NULL);
--